This began when we noticed the health analyzer reporting the following:
[MissingAssembly] Assembly [ProjectSubsiteMaker, Version=126.96.36.199, Culture=neutral, PublicKeyToken=f8132574c3fbdd6f] is referenced in the database [WSS_Content_ITS_Site], but is not installed on the current farm. Please install any feature/solution which contains this assembly. One or more assemblies are referenced in the database [WSS_Content_ITS_Site], but are not installed on the current farm. Please install any feature or solution which contains these assemblies.
After some digging we found that the reference is in the EventReceivers table of the database. This event receiver was part of a custom solution that has been removed, and is associated with a list that no longer exists.
I have tried to find and remove this event receiver through powershell and through the sharepoint UI but it seems that without a list that it is attached to, the event receiver cannot be found. I could just delete the entry from the EventReceiver table in the database but I'm not sure if that would mess up some other reference.
How can we safely remove this event receiver from our database to stop the health analyzer from complaining about it?