solr indexing fails on large mets.xml

Indexing large mets.xml fails because the "content" of the solr document is appended to the URL parameter list. The URL size gets larger than 8192 characters which is forbidden.

Solution: remove the code from MCRSolrPathDocumentFactory#getDocument which handles mets.xml files. There should be no need to append the content to the URL, because the TIKA plugin of solr handles xml quite well.