Revert^2 "Clear the BAL allowlist duration"

Clearing BAL privileges of a PendingIntent only cleared the tokens,
but kept the duration based entries to allow FGS starts. With this
change the duration token is downgraded to NOT allow FGS starts.

`clearAllowBgActivityStarts` is exclusively used by SystemUI
(in NotificationManagerService) and fixing this is part of
fixing a security vulnerability.

The original fix is caused issues when dismissing notifications
from some apps, therefore it is flag guarded now.

This reverts commit 2e971059.
Reason for revert: roll forward with changes

BYPASS_INCLUSIVE_LANGUAGE_REASON=Using an existing API

Bug: 322159724
Flag: com.android.window.flags.bal_clear_allowlist_duration
Test: atest PendingIntentControllerTest
Change-Id: Iac2f9ba4be2dc3addbf04d996c6cb90fe5c6385f