[Panlingual] Removed the feature flag of per app language.

 - App language has already landed, so this flag can be removed.

Bug: b/209775925
Test: Maunal test passed.
Change-Id: Ie3a03ff5d86ab40b210dd26452133b81dbe595df
Merged-In: I6345bfb726234c1dd33dda02d87ca9868725c73c
1 file changed