Fix overreach in <tr>/<li> stripping code

* mw:Param types were also being identified by the tpl/ext test.

  TODO: Audit other uses of DU.isTplOrExtTopLevelNode in the codebase
  and fix uses/helpers.

  In turn, this messed up recursion and deleted <tr> nodes in
  top-level content and introduced dirty diffs in plwiki/Edward_IV_York
  and a few other pages.

Change-Id: I8e4f72ec7c589de9071e0a1bcfc2ac1f89d1c108