Remove special CXPowGate.on. (#5471)

Fixes #3011

Author: MichaelBroughton

cirq-core/cirq/ops/common_gates.py

@@ -1264,19 +1264,6 @@ def __repr__(self) -> str:
             f'global_shift={self._global_shift!r})'
         )
 
-    def on(self, *args: 'cirq.Qid', **kwargs: 'cirq.Qid') -> raw_types.Operation:
-        if not kwargs:
-            return super().on(*args)
-        if not args and set(kwargs.keys()) == {'control', 'target'}:
-            return super().on(kwargs['control'], kwargs['target'])
-        raise ValueError(
-            "Expected two positional argument or else 'target' AND 'control' "
-            "keyword arguments. But got args={!r}, kwargs={!r}.".format(args, kwargs)
-        )
-
-    def __call__(self, *qubits: 'cirq.Qid', **kwargs: 'cirq.Qid'):
-        return self.on(*qubits, **kwargs)
-
 
 def rx(rads: value.TParamVal) -> Rx:
     """Returns a gate with the matrix e^{-i X rads / 2}."""

cirq-core/cirq/ops/common_gates_test.py

@@ -740,47 +740,6 @@ def test_cnot_unitary():
     )
 
 
-def test_cnot_keyword_arguments():
-    a = cirq.NamedQubit('a')
-    b = cirq.NamedQubit('b')
-
-    eq_tester = cirq.testing.EqualsTester()
-    eq_tester.add_equality_group(cirq.CNOT(a, b), cirq.CNOT(control=a, target=b))
-    eq_tester.add_equality_group(cirq.CNOT(b, a), cirq.CNOT(control=b, target=a))
-
-
-def test_cnot_keyword_not_equal():
-    a = cirq.NamedQubit('a')
-    b = cirq.NamedQubit('b')
-
-    with pytest.raises(AssertionError):
-        eq_tester = cirq.testing.EqualsTester()
-        eq_tester.add_equality_group(cirq.CNOT(a, b), cirq.CNOT(target=a, control=b))
-
-
-def test_cnot_keyword_too_few_arguments():
-    a = cirq.NamedQubit('a')
-
-    with pytest.raises(ValueError):
-        _ = cirq.CNOT(control=a)
-
-
-def test_cnot_mixed_keyword_and_positional_arguments():
-    a = cirq.NamedQubit('a')
-    b = cirq.NamedQubit('b')
-
-    with pytest.raises(ValueError):
-        _ = cirq.CNOT(a, target=b)
-
-
-def test_cnot_unknown_keyword_argument():
-    a = cirq.NamedQubit('a')
-    b = cirq.NamedQubit('b')
-
-    with pytest.raises(ValueError):
-        _ = cirq.CNOT(target=a, controlled=b)
-
-
 def test_cnot_decompose():
     a = cirq.NamedQubit('a')
     b = cirq.NamedQubit('b')