remove extra User-Agent prefix in the ionq API header (#6232)

* remove the extra User-Agent prefix

* require ionq User-Agent starts with "cirq/"

---------

Co-authored-by: Pavol Juhas <juhas@google.com>

Author: splch

cirq-ionq/cirq_ionq/ionq_client.py

@@ -291,7 +291,7 @@ def _user_agent(self):
         """
         cirq_version_string = f'cirq/{cirq_version}'
         python_version_string = f'python/{platform.python_version()}'
-        return f'User-Agent: {cirq_version_string} ({python_version_string})'
+        return f'{cirq_version_string} ({python_version_string})'
 
     def _target(self, target: Optional[str]) -> str:
         """Returns the target if not None or the default target.

cirq-ionq/cirq_ionq/ionq_client_test.py

@@ -84,6 +84,7 @@ def test_ionq_client_attributes():
         'Content-Type': 'application/json',
         'User-Agent': client._user_agent(),
     }
+    assert client.headers['User-Agent'].startswith('cirq/')
     assert client.default_target == 'qpu'
     assert client.max_retry_seconds == 10
     assert client.verbose is True

cirq-ionq/cirq_ionq/ionq_devices_test.py

@@ -88,8 +88,3 @@ def test_validate_circuit_valid():
             gate_domain={gate: gate.num_qubits() for gate in VALID_GATES},
         )
         device.validate_circuit(circuit)
-
-
-def test_decompose_operation_deprecated():
-    with cirq.testing.assert_deprecated('Use cirq.optimize_for_target_gateset', deadline='v0.16'):
-        _ = ionq.decompose_to_device(cirq.CZ(*cirq.LineQubit.range(2)))