Revert "[BEAM-5878] support DoFns with Keyword-only arguments (#9237)"

This reverts commit 0c2d8be.

sdks/python/apache_beam/internal/pickler.py

@@ -136,31 +136,6 @@ def _reject_generators(unused_pickler, unused_obj):
 
 dill.dill.Pickler.dispatch[types.GeneratorType] = _reject_generators
 
-# TODO: Remove this once uqfoundation/dill#313 is fixed
-if sys.version_info[0] > 2:
-  # Monkey patch for dill._dill.Pickler to pickle functions
-  # with keyword-only args
-  _create_function = dill.dill._create_function
-
-  def _create_function_has_kwdefaults(fcode, fglobals, fname=None,
-                                      fdefaults=None, fclosure=None, fdict=None,
-                                      fkwdefaults=None):
-    func = _create_function(fcode, fglobals, fname, fdefaults, fclosure, fdict)
-    func.__kwdefaults__ = fkwdefaults
-    return func
-
-  def new_save_reduce(self, func, args, *other_args, **kwargs):
-    pickler = super(dill.dill.Pickler, self)
-    obj = kwargs['obj'] if 'obj' in kwargs else None
-    if (func is _create_function and obj is not None
-        and getattr(obj, '__kwdefaults__', None) is not None):
-      pickler.save_reduce(_create_function_has_kwdefaults,
-                          args + (getattr(obj, '__kwdefaults__', None),),
-                          *other_args, **kwargs)
-    else:
-      pickler.save_reduce(func, args, *other_args, **kwargs)
-
-  dill._dill.Pickler.save_reduce = new_save_reduce
 
 # This if guards against dill not being full initialized when generating docs.
 if 'save_module' in dir(dill.dill):