Remove lastgenre separator config

Author: snejus

beetsplug/lastgenre/__init__.py

@@ -111,7 +111,6 @@ def __init__(self) -> None:
                 "force": False,
                 "keep_existing": False,
                 "auto": True,
-                "separator": ", ",
                 "prefer_specific": False,
                 "title_case": True,
                 "pretend": False,

docs/plugins/lastgenre.rst

@@ -191,16 +191,6 @@ file. The available options are:
   Default: ``no``.
 - **source**: Which entity to look up in Last.fm. Can be either ``artist``,
   ``album`` or ``track``. Default: ``album``.
-- **separator**:
-
-  .. deprecated:: 2.6
-
-      The ``separator`` option is deprecated. Genres are now stored as a list in
-      the ``genres`` field and written to files as individual genre tags. This
-      option has no effect and will be removed in a future version.
-
-  Default: ``', '``.
-
 - **whitelist**: The filename of a custom genre list, ``yes`` to use the
   internal whitelist, or ``no`` to consider all genres valid. Default: ``yes``.
 - **title_case**: Convert the new tags to TitleCase before saving. Default: