Remove flag brightness_int_range_user_perception

The flag has never been fully enabled. Another solution was implemented, see go/set-brightness-percentage.

Bug: 429405130
Test: DisplayPowerControllerTest, DisplayManagerServiceTest, BrightnessSynchronizerTest
Flag: EXEMPT removing com.android.server.display.feature.flags.brightness_int_range_user_perception
Change-Id: I54cb98ce06728625a0815118f22403acc81a2145