Ignore vendor apex priv-app permission allowlists

Apexes contain the allowlists for privileged permissions used by their
respective apk's, however vendor (partner) apexes should be forbidden from
using this mechanism.

Test: atest FrameworksServicesTests:SystemConfigTest
Bug: 190375768
Change-Id: I34bf2a80fb66f2b2a732234111a338e3af1e919b