Remove untrusted app access to /proc/net

This change is for testing potential app-compat issues when removing
access to file in /proc/net. See: b/114475727#comment11.

Bug: 114475727
Test: build/boot taimen.
Test: atest CtsLibcoreOjTestCases
Test: FileSystemPermissionTest
Test: ListeningPortsTest b/114772424
Change-Id: I1db1c2b41308e47c9ec9db57ea8597a650c8906d
(cherry picked from commit 6784f80b)