Splits the dropping of image.img_user_timestamp (which was added
in MW 1.29) from patch-drop-image-img_user_timestamp.sql because
if you're upgrading from a much older MW version, the index may
not exist, and will cause the whole
patch-drop-image-img_user_timestamp.sql patch to fail from the
index not existing.
It probably should have been added by the ifTableNotExists/actor
entry with patch-image-user-index-2.sql (as actor wasn't added
until 1.31)...
Also fix up some comments relating to the patch filenames I
missed whilst I split them in T257407.
Bug: T267543
Change-Id: I3cdecf6df459d44b4d51a9ad9e1ff00997ff0c02
