changelog/thanks for #217
python-musicbrainz-ngs 0.3 is out!
mbcollection: use library functions

Since we now require python-musicbrainz-ngs 0.3 or later, we no longer have to
hand-craft the API requests.
remove py-mb-ngs version conditional

Another code simplification due to requiring python-musicbrainz-ngs 0.3 or
later.