Don't shared oem-defined libs to vendor apks

OEM-defined libs in /system/etc/public.libraries-<companyname>.txt files
are not available to apks in the vendor partition, otherwise we are
allowing vendor -> system dependency, which is a Treble violation.

Bug: 71561542
Test: mm -j under system/core/libnativeloader/test and runtest.sh
the four libs (lib[foo|bar].[oem1|oem2].so are all loaded in
android.app.test.system app but not in android.app.test.vendor app

Change-Id: Ie5d9160ae4dc2a64beb6507602ee5a1db6518875