Reapply "CertPinInstallReceiver: remove files at boot time"

The CertPinInstallReceiver is now executed only by the system user.

This reverts commit fffe3a08.

Test: Boot, create secondary user. No crash detected.
Test: Install with flag disabled; check that pins file is available.
      Enable platform flag and reboot. The pins file and its metadata
      are gone.
Bug: 391205997
Bug: 400583133
Flag: com.android.server.flags.certpininstaller_removal
Change-Id: Ie9542b50a45072bd5e5bf30c55e08260b3ef6a8e