remove system_server debugfs:file r_file_perms

Auditallow added in commit 72edbb3e ("Audit generic debugfs access for
removal", May 01 2018) has not triggered. Remove allow rule and tighten
up neverallow rule.

Test: policy compiles
Test: no collected SELinux denials.
Change-Id: I9a90463575f9eab4711b72d6f444fa9d526b80e1