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

rootdir/ueventd.rc

@@ -37,8 +37,6 @@ subsystem dma_heap
 /dev/tty                  0666   root       root
 /dev/random               0666   root       root
 /dev/urandom              0666   root       root
-# Make HW RNG readable by group system to let EntropyMixer read it.
-/dev/hw_random            0440   root       system
 /dev/ashmem*              0666   root       root
 /dev/binder               0666   root       root
 /dev/hwbinder             0666   root       root