neverallow some /proc file reads

Lock in the gains we've made so far in restricting access to generically
labeled /proc files. There's more we can do here, but let's avoid
inadvertent regressions.

Test: policy compiles. Only compile time assertions added.
Bug: 26813932
Change-Id: If354c2ddc1c59beed7f0eb4bcbd3f0d9971c3b8a