writerfilter: remove mce token generator

Commit af7d4a5ebf3e6a09cd2079f241dee16aa22e0276 (n#820503: initial MCE
support in writerfilter ooxml tokenizer, 2013-07-03) added these, but in
fact only the namespace-alias part was necessary. Now that oox provides
the list of namespaces to be registered, it can be removed completely.

Change-Id: If8f1b0c07602a0170c63b53d806a5b466d485747