testsuite: remove unused parameter

Problem: In t0005-kvs.py the helper function set_and_check_context()
has a 'msg' parameter that is never used in the function.

Remove the unused parameter.

Author: chu11

t/python/t0005-kvs.py

@@ -31,7 +31,7 @@ def test_kvs_dir_open(self):
         with flux.kvs.get_dir(self.f) as d:
             self.assertIsNotNone(d)
 
-    def set_and_check_context(self, key, value, msg=""):
+    def set_and_check_context(self, key, value):
         kd = flux.kvs.KVSDir(self.f)
         kd[key] = value
         kd.commit()