def _remove_observation(self, x_to_remove, y_to_remove):
self._remove_observation_from_variances(x_to_remove, y_to_remove)<EOL>self._remove_observation_from_means(x_to_remove, y_to_remove)<EOL>self.window_size -= <NUM_LIT:1><EOL>
Remove observation from window, updating means/variance efficiently.