If onegrid is on we don't check if destination db is new or not

We just migrate them using the special case where everything shifts up
if we meet the criteria

Bug: 392978014
Test: GridSizeMigrationTest
Flag: com.android.launcher3.one_grid_specs
Change-Id: I4efda781d6fbe6f3e1854b22685abd1b923c3dc4