Do not check user/group names in pwd/grp tests for OEM uid/gids

Vendors that use config.fs will have their own uniquely named
user/group names for uids/gids that fall in the OEM ranges.  We
continue to allow lookup via oem_## for these values, however the
returned structs will always include the name from config.fs, so we do
not check it for anything in the tests.

Bug: 77549259
Test: bionic unit tests with uid 5000 as AID_CRAS
Change-Id: I27fc1fdd0e22063fea82b4c9d2a6fb8b865c5d7b