remove singlehtml_sidebars shim (#119)

CHANGES.rst

@@ -10,6 +10,8 @@ Unreleased
     versions are no longer required for the banner to be correct. :pr:`117`
 -   Generate 404 page using the sphinx-notfound-page extension. This fixes the
     URLs when the page is hosted so that it loads the CSS. :issue:`34`
+-   Remove handling for ``singlehtml_sidebars`` config which predated Sphinx's
+    support. :pr:`119`
 
 
 Version 2.1.3

src/pallets_sphinx_themes/__init__.py

@@ -9,7 +9,6 @@
 
 from sphinx.application import Sphinx
 from sphinx.builders.dirhtml import DirectoryHTMLBuilder
-from sphinx.builders.singlehtml import SingleFileHTMLBuilder
 from sphinx.errors import ExtensionError
 
 from .theme_check import only_pallets_theme
@@ -55,13 +54,6 @@ def setup(app):
     except ExtensionError:
         pass
 
-    try:
-        app.add_config_value("singlehtml_sidebars", None, "html")
-    except ExtensionError:
-        pass
-    else:
-        app.connect("builder-inited", singlehtml_sidebars)
-
     from .themes import click as click_ext
     from .themes import jinja as jinja_ext
 
@@ -124,19 +116,6 @@ def canonical_url(app: Sphinx, pagename, templatename, context, doctree):
     context["pageurl"] = base + target
 
 
-@only_pallets_theme()
-def singlehtml_sidebars(app):
-    """When using a ``singlehtml`` builder, replace the
-    ``html_sidebars`` config with ``singlehtml_sidebars``. This can be
-    used to change what sidebars are rendered for the single page called
-    ``"index"`` by the builder.
-    """
-    if app.config.singlehtml_sidebars is not None and isinstance(
-        app.builder, SingleFileHTMLBuilder
-    ):
-        app.config.html_sidebars = app.config.singlehtml_sidebars
-
-
 @only_pallets_theme()
 def skip_internal(app, what, name, obj, skip, options):
     """Skip rendering autodoc when the docstring contains a line with