brillo: Rely on static SELinux policy for camera

In Brillo, there are no applications, and SELinux policy can be
configured statically (at build time).  In this model, we control
access to the camera binder, and thus to the camera stack.

Bug: 26936651
Test: Brillo test camera client can connect to camera

Change-Id: I5207c2f78e4f36778b90aac29bf4317b62cbd3dd