CLN: Replace sphinx's rpartition with python's in-built one (#43360)

Author: bodevone

doc/source/conf.py

@@ -461,7 +461,6 @@
 # eg pandas.Series.str and pandas.Series.dt (see GH9322)
 
 import sphinx  # isort:skip
-from sphinx.util import rpartition  # isort:skip
 from sphinx.ext.autodoc import (  # isort:skip
     AttributeDocumenter,
     Documenter,
@@ -521,8 +520,8 @@ def resolve_name(self, modname, parents, path, base):
             # HACK: this is added in comparison to ClassLevelDocumenter
             # mod_cls still exists of class.accessor, so an extra
             # rpartition is needed
-            modname, accessor = rpartition(mod_cls, ".")
-            modname, cls = rpartition(modname, ".")
+            modname, _, accessor = mod_cls.rpartition(".")
+            modname, _, cls = modname.rpartition(".")
             parents = [cls, accessor]
             # if the module name is still missing, get it like above
             if not modname: