Remove manual pregrants for SystemCaptionsService (handled via roles)

DefaultPermissionGrantPolicy was granting the RECORD_AUDIO permission
to the package that provides SystemCaptionsService. This permission is
already managed via roles; specifically it is set in the
`SYSTEM_AUDIO_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: I57be6ca431aa00b01ddb14674f555999cdf13acf