docs: Remove unneeded backslash escapes

Python 3.x was emitting a DeprecationWarning. AFAICT there has been no
impact on the HTML rendering.

mitogen/core.py

@@ -374,7 +374,7 @@ def io_op(func, *args):
 
     :returns:
         Tuple of `(return_value, disconnected)`, where `return_value` is the
-        return value of `func(\*args)`, and `disconnected` is :data:`True` if
+        return value of `func(*args)`, and `disconnected` is :data:`True` if
         disconnection was detected, otherwise :data:`False`.
     """
     while True:

mitogen/parent.py

@@ -1256,7 +1256,7 @@ class CallChain(object):
 
     def call_async(self, fn, *args, **kwargs):
         """
-        Arrange for `fn(\*args, \**kwargs)` to be invoked on the context's main
+        Arrange for `fn(*args, **kwargs)` to be invoked on the context's main
         thread.
 
         :param fn: