Merge branch 'no_obsolete' into 'master'

Add argument to remove unused translations when running makemessages

See merge request thalia/concrexit!893

website/thaliawebsite/settings/settings.py

@@ -320,3 +320,6 @@ DEFAULT_EXCEPTION_REPORTER_FILTER = (
 
 # Make sure the locations in django.po files don't include line nrs.
 makemessages.Command.xgettext_options.append('--add-location=file')
+
+# Remove unused translations.
+makemessages.Command.xgettext_options.append('--no-obsolete')