Don't check OverrideAllowedState

Don't check OverrideAllowedState when calling remove overrides and there
are no overrides.
This fixes failure in CompatChangesTest (tried to clear non existing
overrides for a logging only change).
Also fixed return value of removeOverride to return the correct thing.

Test: atest  com.android.server.compat.CompatConfigTest
Test: atest  android.app.compat.CompatChangesTest
Bug: 151421544
Change-Id: I9c63f332337bc465115556fbc6f0b40fb7e102da