Clean up fully rolled out PermissionMigrationForZeroTrustImplEnabled

Flag was rolled out in Android V.

Bug: 364998990
Test: TH
Flag: EXEMPT flag cleanup
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:dfdf7fb5acd44bcccb2d119793727683fe1654a7)
Merged-In: I25f472268b075d79cc0a0378a55b515694109cbe
Change-Id: I25f472268b075d79cc0a0378a55b515694109cbe
2 files changed