Excel Mobile Viewer Feature removal troubles in 2013 upgrade

Question

I am in the process of upgrading from SharePoint Server 2007 to Server 2013, and Excel Web Services is throwing a spanner in the gears.

I have 3 environments:

SharePoint 2007 (SQL 2005) in production SharePoint 2010 (SQL 2008) test SharePoint 2013 (SQL 2014) test

I make backups from the 2007 environment, copy to the 2010 environment, create web spplications and mount them with this script:

#Create web app with dummy db (dummy db is needed for db upgrade)
#New-SPWebApplication -Name $WebAppName -Port $WebAppPort -HostHeader $WebAppHostHeader -URL ("http://" + $WebAppHostHeader) -ApplicationPool $WebAppAppPool -DatabaseName $WebAppDatabaseNameDeleteMe -DatabaseServer $WebAppDatabaseServer

#Remove new empty content DB
Get-SPContentDatabase $WebAppDatabaseNameDeleteMe | Remove-SPContentDatabase

#Add old content DB
Mount-SPContentDatabase $WebAppDatabaseNameMountMe -DatabaseServer $WebAppDatabaseServer -WebApplication $WebAppName

So far so good. No problem. Same procedure - backup from the 2010 environment, copy to the 2013 environment, run:

#Create web app with dummy db (dummy db is needed for db upgrade)
New-SPWebApplication -Name $WebAppName -Port $WebAppPort -HostHeader $WebAppHostHeader -URL ("http://" + $WebAppHostHeader) -ApplicationPool $WebAppAppPool -AuthenticationMethod NTLM -DatabaseName $WebAppDatabaseNameDeleteMe -DatabaseServer $WebAppDatabaseServer

#Remove new empty content DB
Get-SPContentDatabase $WebAppDatabaseNameDeleteMe | Remove-SPContentDatabase

#Add old content DB
Mount-SPContentDatabase $WebAppDatabaseNameMountMe -DatabaseServer $WebAppDatabaseServer -WebApplication $WebAppName

Now I get this error:

09/16/2015 13:05:35.66 powershell (0x139C) 0x0D9C SharePoint Foundation Upgrade SPContentDatabaseSequence ajxkg INFO SPContentDatabase Name=SPdatabase d4ba3004-26aa-4739-9d21-d03b4b033160 09/16/2015 13:05:35.66 powershell (0x139C) 0x0D9C SharePoint Foundation Upgrade SPContentDatabaseSequence ajxkg ERROR Found a missing feature Id = [e995e28b-9ba8-4668-9933-cf5c146d7a9f], Name = [Excel Mobile Viewer Feature], Description = [Adds site-level Excel Mobile Viewer Feature to the Microsoft SharePoint Foundation framework], Install Location = [MobileExcelWebAccess] d4ba3004-26aa-4739-9d21-d03b4b033160 09/16/2015 13:05:35.70 powershell (0x139C) 0x0D9C SharePoint Foundation Upgrade SPContentDatabaseSequence ajxkh INFO SPContentDatabase Name=SPdatabase d4ba3004-26aa-4739-9d21-d03b4b033160 09/16/2015 13:05:35.70 powershell (0x139C) 0x0D9C SharePoint Foundation Upgrade SPContentDatabaseSequence ajxkh ERROR The feature with Id e995e28b-9ba8-4668-9933-cf5c146d7a9f is referenced in the database [SPdatabase], but is not installed on the current farm. The missing feature may cause upgrade to fail. Please install any solution which contains the feature and restart upgrade if necessary. d4ba3004-26aa-4739-9d21-d03b4b033160

OK, back to the SP2010 farm, run Uninstall-SPFeature, then Get-SPSite http://mysSPsite | Get-SPWeb -Limit ALL |%{ Get-SPFeature -Web $_ } | Select DisplayName,ID -Unique |out-file c:\spresult\spresult.txt

And:

DisplayName                             Id                                     
-----------                             --                                     
WebPageLibrary                          00bfea71-c796-4402-9f2f-0eb9a6e71b18   
IssuesList                              00bfea71-5932-4f9c-ad71-1557e5751100   
WorkflowHistoryList                     00bfea71-4ea5-48d4-a4ad-305cf7030140   
NoCodeWorkflowLibrary                   00bfea71-f600-43f6-a895-40c0de7b0117   
SurveysList                             00bfea71-eb8a-40b1-80c7-506be7590102   
GridList                                00bfea71-3a1d-41d3-a0ee-651d11570120   
GanttTasksList                          00bfea71-513d-4ca0-96c2-6a47775c0119   
LinksList                               00bfea71-2062-426c-90bf-714c59600103   
MobilityRedirect                        f41cc668-37e5-4743-b4a8-74d1db3fd8a4   
workflowProcessList                     00bfea71-2d77-4a75-9fca-76516689e21a   
TasksList                               00bfea71-a83e-497e-9ba0-7a5c597d0107   
TeamCollab                              00bfea71-4ea5-48d4-a4ad-7ea5c011abe5   
AnnouncementsList                       00bfea71-d1ce-42de-9c63-a44004ce0104   
PictureLibrary                          00bfea71-52d4-45b3-b544-b1c71b620109   
ContactsList                            00bfea71-7e6d-4186-9ba8-c047ac750105   
CustomList                              00bfea71-de22-43b2-a848-c05709900100   
DocumentLibrary                         00bfea71-e717-4e80-aa17-d0c71b360101   
DiscussionsList                         00bfea71-6a49-43fa-b535-d15c05500108   
DataSourceLibrary                       00bfea71-f381-423d-b9d1-da7a54c50110   
ExternalList                            00bfea71-9549-43f8-b978-e47e54a10600   
EventsList                              00bfea71-ec85-4903-972d-ebe475780106   
XmlFormLibrary                          00bfea71-1e1d-4562-b56a-f05371bb0115   
TransMgmtLib                            29d85c25-170c-4df9-a641-12db0b9d4130   

No Excel Web Services. Backup 2010 content db, copy to 2013, dismount the db in SharePoint, restore of the content db with overwrite, mount the fresh copy, but still it still claims that Excel Mobile Viewer Feature is present.

So, any suggestions?