Move enforceCrossUser*Permission() back into PackageManagerService.

The three methods aren't part of permission management, but instead
they are only called by PackageManagerService as a utility method
containing a specific series of checks it needs for its own business
logic. So these shouldn't be permission APIs and thus moving them
back.

This leaves a simplified copy of enforceCrossUserPermission() inside
PermissionManagerService for its own usage, and it seems fine because
different system services have different needs for cross user
permission checking (See cs/enforceCrossUserPermission). If we ever
want to have a unified method for cross user permission checking, it
should be on a higher level component, e.g. Context.

Bug: 158736025
Test: presubmit
Change-Id: Ic1ebc5d83c8c9e854bd6fbff7dbbb7f2e07d613d