mbcollection: Fix default 'remove' value.
If the default is not None the value cannot be overriden by the user's
config.yaml.
@@ -113,7 +113,7 @@ class MusicBrainzCollectionPlugin(BeetsPlugin):
help=u'Update MusicBrainz collection')
mbupdate.parser.add_option('-r', '--remove',
action='store_true',
- default=False,
+ default=None,
dest='remove',
help='Remove albums not in beets library')
mbupdate.func = self.update_collection
