remove "self:process ptrace" from domain, netd neverallow rules

Remove "self:process ptrace" from all SELinux enforced domains.
In general, a process should never need to ptrace itself.
We can add this back to more narrowly scoped domains as needed.

Add a bunch of neverallow assertions to netd.te, to verify that netd
never gets unexpected capabilities.

Change-Id: Ie862dc95bec84068536bb64705667e36210c5f4e