Remove special config for /dev/hw_random.

There's no need for system_server to access this any more, so no need to
have weaker permissions than we'll get by default (ignoring the fact
that SELinux policy is our real protection here anyway).

Bug: http://b/179086242
Test: treehugger
Change-Id: I584e87f027f44e10190c2e5c2eb85785f61f8bd5