Remove custom cirq_type (quantumlib#5249)

Custom `cirq_type` was deprecated in quantumlib#4704 and not necessary for internal types.

Author: dabacon

cirq-core/cirq/ops/boolean_hamiltonian.py

@@ -76,7 +76,6 @@ def _value_equality_values_(self) -> Any:
 
     def _json_dict_(self) -> Dict[str, Any]:
         return {
-            'cirq_type': self.__class__.__name__,
             'parameter_names': self._parameter_names,
             'boolean_strs': self._boolean_strs,
             'theta': self._theta,