Remove manual pregrants for AttentionService (handled via roles)

AttentionService requires the CAMERA permission. This permission is
already managed via roles; specifically it is set in the
`SYSTEM_VISUAL_INTELLIGENCE` role in
PermissionController/res/xml/roles.xml. Therefore the code performing
the pre-grant manually in DefaultPermissionGrantPolicy can be removed.

Bug: 222231605
Test: adb shell dumpsys package com.google.android.as
Test: atest GtsPermissionTestCases:com.google.android.permission.gts.DefaultPermissionGrantPolicyTest#testDefaultGrantsWithRemoteExceptions
Change-Id: Ie5db64ef13a1b0258fa3f48f8d2cf05fffe7af66