Remove checking for proportional and delta2

Author: Jacobluke-

dabest/_dabest_object.py

@@ -501,9 +501,6 @@ def _check_errors(self, x, y, idx, experiment, experiment_label, x1_level):
                 error_msg = "If `delta2` is True. `x` parameter cannot be None. String or list expected"
                 raise ValueError(error_msg)
 
-            if self.__proportional:
-                err0 = "`proportional` and `delta2` cannot be True at the same time."
-                raise ValueError(err0)
 
             # idx should not be specified
             if idx: