Remove a check for AIDs in the OEM range.

Remove the check that AIDs in the OEM range are not defind in
android_filesystem_config, as we do not yet have a good solution for
OEMs to define custom AIDs and what OEMs are currently doing isn't
hurting anything.

Bug: b/64137613
Test: pwd.getpwent_iterate / grp.getgrent_iterate
Change-Id: If98ad4443fe9e827e3f17b3df92eca82763e6290