Get rid of env parameter from some DOMUtils helpers

* Moved aboutId tests from the MWEnvironment object to Util
  to eliminate unnecessary dependency on the env object in
  various helpers.

* This lets me remove env from a whole bunch of dependent calls
  and in a future patch, will let me tweak the isNewElt helper
  without needing to pass the env object from everywhere.

Change-Id: Ia855f9e56ce58d87539682454c47fc6cb6306336