Remove AlwaysRotateDisplayDevice feature flag

This feature was used to always read WindowManager rotation instead of
respecting FLAG_ROTATES_WITH_CONTENT. It has been enabled in production
for a while now and is stable.
This CL removes the feature flag.

Bug: 409609172
Test: atest LogicalDisplayMapperTest
Flag: EXEMPT removing flag does not require flag
Change-Id: Iea22789e74bc5daae757a0cc635a6eacb6f3b96a