I believe you can hide them by changing the content type in the Library settings.
Go to Library Settings > Advanced Settings > Content Types
"Allow Management of content types." -> Yes
A new section will appear in the library settings. Select your document/item/object of interest. In this case I'll edit a Document.
You should see two columns that relate to the
% Complete and
Task Status. Go into each of them and set them to
Hidden. Here I'm doing an example with the
Changing the setting to Hidden.
Now when you edit the document properties or item properties, the respective item is no longer shown.
If you've got access to InfoPath you can change it with the button. Then select the sections to remove, and do a quick publish at the top left of the InfoPath Designer window.
_spBodyOnLoadFunctionNames.push( "removeObjects" );
$('.ms-formtable tr:contains("% Complete")').hide()
$('.ms-formtable tr:contains("Task Status")').hide()