Move sepolicy and recovery from on-device tree and add dependency.

Prevent sepolicy and sepolicy.recover from showing up in the root
filesystem when they will not be created as part of it.  Also make
sure both are added as dependencies to version_policy to ensure the
neverallow checks are run.

Bug: 31363362
Test: Builds and boots, including recovery, without additional
  denials.  Neverallow violations still caught at build time.

Change-Id: I39e3cbc150551c9316952523927d057538cd00a7