[sestarnix] Remove .pp suffix from binary policy filenames

The .pp suffix refers to policy "packages", which are bundles of
policy data of various types.  Binary policies are typically named
with a version suffix (e.g. "policy.33") or no suffix.

Migrate the compiled policies to that naming scheme and update all
tests, and update the README.md to recommend the compile_policies
script be used to rebuild them.

Change-Id: I9600daa06209a81cc4de6aa40e79fbedab67b0b2
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1593128
Reviewed-by: Jean-François Geyelin <jif@google.com>
Fuchsia-Auto-Submit: Wez <wez@google.com>
Commit-Queue: Wez <wez@google.com>