parserTests selser-change gen fix: mw:Entity spans are uneditable

* mw:Entity spans can only edited as a subtree, i.e. the whole
  entity can be deleted, or a new entity can be added. It is not
  possible to leave the wrapper span around without contents.

* So, updating our selser change generation to reflect that. This
  eliminates the possibility of having to deal with mw:DiffMarker
  metas inside entities and skip them.

Change-Id: Ic1387421a8d4a419cc4b028ad4021b317c871948