Extract ActiveAdmin and DevicePolicyData from DPMS.

And some minor changes:

* Don't check uid of admin returned by PackageManager since
it would only happen as a result of a horrible bug and looks
defensive.

* Don't check CrossUserPermission and feature flag in findAdmin
since it is only invoked from already trusted low level context
and not exposed via binder.

* Some redundant null checks.

* Inclusive language.

* Removed non-standard indentation in dupm() methods, replaced
  by newlines. Also added some missing spaces.

Test: presubmit
Bug: 162317175
Change-Id: Ib30787d5205235f33e350e0e66b390940b723bca