:meth:`.WSignalSourceProto.remove_callback` implementation

def remove_callback(self, signal_name, callback):
		""" :meth:`.WSignalSourceProto.remove_callback` implementation
		"""
		try:
			self.__direct_callbacks[signal_name].remove(callback)
		except KeyError:
			raise ValueError('Signal "%s" does not have the specified callback' % signal_name)