Remove legacy database upgrade paths in AppWidgetServiceImpl.

The database upgrades deal with the multi user change from Android 4 to 5.
No modern device can have a database with the old format and the code is
confusing, so needs to be removed.

Bug: 378518205
Test: AppWidgetServiceImplTest
Flag: EXEMPT code cleanup
Change-Id: Ibe7ea033433d856b501f4006d0ce56fd95472eeb