quodlibet: 4.2.0 -> 4.2.1

Semi-automatic update generated by
https://github.com/ryantm/nixpkgs-update tools. This update was made
based on information from
https://repology.org/metapackage/quodlibet/versions

Also remove intltool and start running tests, changes missed in 4.2.0 update.

Also do not collect TReplayGain for variants without gst-plugins-good.