ve.dm.MWTransclusionModel: Clean up and fix logic error

* Reduce duplication by calling #removePart (equal, line by line)
* Reset `remove` at the start of each iteration, it was leaking
  through to future iterations.
* Minor simplification in property access.

Change-Id: Ie0a83d582804bc50131ca5a8da36b0605dd4a6c3
Merge "ve.dm.MWTransclusionModel: Clean up and fix logic error"