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