remove system_app proc_net_type access

The auditallow added in 7a4af30b has not triggered. This is safe to
remove.

Test: device boots and no obvious problems.
Test: No audit messages seen since May 2018 on go/sedenials
Bug: 9496886
Bug: 68016944
Change-Id: I3861b462467e1fc31e67a263ad06716a4111dcb8

private/system_app.te

@@ -110,13 +110,6 @@ allow system_app keystore:keystore_key {
     user_changed
 };
 
-# /proc/net access.
-# TODO(b/9496886) Audit access for removal.
-r_dir_file(system_app, proc_net_type)
-userdebug_or_eng(`
-  auditallow system_app proc_net_type:{ dir file lnk_file } { getattr open read };
-')
-
 # settings app reads /proc/version
 allow system_app {
   proc_version