Cleanup separatePermissionNotifications flag

This removes the public separatePermissionNotificationsEnabled()
(which is always true now) method and code that relies on it.

PermissionManager now exports just the PIC key for caches.  The NOTIFY
constant is no longer used and has been removed.

In AudioService Conditions on separatePermissionNotificationsEnabled()
are collapsed given that the method always returns true.  There is a
small clean up in setupPermissionListener() per review comments.

Flag: EXEMPT removing android.app.pic_separate_permission_notifications
Bug: 423886240
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: I14b0b483b6180d59479b30c36356893214254f9b