Cleanup PIC flags

This removes non-exported PIC flags that have been deployed in 25Q2 or
earlier, and removes any code that is guarded by the flags.

This removes pic_isolated_cache_statistics, which was never deployed.

The public PIC method separatePermissionNotificationsEnabled() is
retained because several external classes reference it.

Flag: EXEMPT removing android.app.pic_uses_shared_memory
Flag: EXEMPT removing android.app.pic_cache_nulls
Flag: EXEMPT removing android.app.pic_isolate_cache_by_uid
Flag: EXEMPT removing android.app.pic_separate_permission_notifications
Flag: EXEMPT removing android.app.pic_isolated_cache_statistics
Bug: 423886240
Bug: 423987010
Bug: 423972381
Test: atest
 * CtsAppEnumerationTestCases
 * CtsMediaAudioPermissionTestCases
 * CtsMediaAudioTestCases:AudioRecordTest
 * CtsOsTestCases:IpcDataCacheTest
 * FrameworksCoreTests:IpcDataCacheTest
 * FrameworksCoreTests:PropertyInvalidatedCacheTests
 * ServiceBluetoothTests
 * android.app.appops.cts.AppOpsLoggingTest
 * android.content.pm.cts.PackageManagerTest
 * android.media.audio.cts.AudioFocusTest
 * com.android.server.pm.PackageManagerTests

Change-Id: Ifa4b0381b1818cb2f3e010df8f80d699bd576bcb