[piav2] Dont check for "no_install_unknown_sources" for installs from privileged sources.

Installs from privileged sources should only check for "no_install_apps"
retriction.

This was implemented in PiaV1 in ag/27495994

Bug: 324305636
Test: Manual. Follow repro steps in the bug
Flag: android.content.pm.use_pia_v2

Change-Id: I6004baa8d7a8cbcc9b89e5c0286a5846bd896902