py3: Use list comprehensions instead of filter()

This is just a stylistic change, and is not strictly required for Python 3
compat.

mopidy/backend/dummy.py

@@ -44,7 +44,7 @@ class DummyLibraryProvider(backend.LibraryProvider):
         return self.dummy_find_exact_result
 
     def lookup(self, uri):
-        return filter(lambda t: uri == t.uri, self.dummy_library)
+        return [t for t in self.dummy_library if uri == t.uri]
 
     def refresh(self, uri=None):
         pass

mopidy/core/tracklist.py

@@ -334,10 +334,10 @@ class TracklistController(object):
                 # Fail hard if anyone is using the <0.17 calling style
                 raise ValueError('Filter values must be iterable: %r' % values)
             if key == 'tlid':
-                matches = filter(lambda ct: ct.tlid in values, matches)
+                matches = [ct for ct in matches if ct.tlid in values]
             else:
-                matches = filter(
-                    lambda ct: getattr(ct.track, key) in values, matches)
+                matches = [
+                    ct for ct in matches if getattr(ct.track, key) in values]
         return matches
 
     def move(self, start, end, to_position):

mopidy/mpd/translator.py

@@ -59,13 +59,13 @@ def track_to_mpd_format(track, position=None):
     if track.album is not None and track.album.artists:
         artists = artists_to_mpd_format(track.album.artists)
         result.append(('AlbumArtist', artists))
-        artists = filter(
-            lambda a: a.musicbrainz_id is not None, track.album.artists)
+        artists = [
+            a for a in track.album.artists if a.musicbrainz_id is not None]
         if artists:
             result.append(
                 ('MUSICBRAINZ_ALBUMARTISTID', artists[0].musicbrainz_id))
     if track.artists:
-        artists = filter(lambda a: a.musicbrainz_id is not None, track.artists)
+        artists = [a for a in track.artists if a.musicbrainz_id is not None]
         if artists:
             result.append(('MUSICBRAINZ_ARTISTID', artists[0].musicbrainz_id))