remove _idle_wires function

qiskit/transpiler/passes/routing/utils.py

@@ -79,7 +79,7 @@ def route_cf_multiblock(tpass, cf_opnode, current_layout, qregs, root_dag, seed=
                 ]
                 virtual_swap_dag.compose(physical_swap_dag, qubits=order)
                 updated_dag_block.compose(virtual_swap_dag)
-        idle_qubits[i] = _qubit_wires(updated_dag_block.idle_wires())
+        idle_qubits[i] = set(root_dag.qubits) & set(updated_dag_block.idle_wires())
     cfop_idle_qubits = set.intersection(*map(set, idle_qubits))
     # contract idle bits from full width post routing
     for i, updated_dag_block in enumerate(block_dags):
@@ -149,7 +149,7 @@ def route_cf_looping(tpass, cf_opnode, current_layout, root_dag, seed=None):
         virtual_swap_dag.compose(physical_swap_dag, qubits=order)
         updated_dag_block.compose(virtual_swap_dag)
     # contract from full width post routing
-    idle_qubits = _qubit_wires(updated_dag_block.idle_wires())
+    idle_qubits = set(root_dag.qubits) & set(updated_dag_block.idle_wires())
     updated_dag_block.remove_qubits(*idle_qubits)
     new_dag_block = DAGCircuit()
     new_num_qubits = updated_dag_block.num_qubits()
@@ -179,18 +179,3 @@ def combine_permutations(*permutations):
     for this_order in permutations[1:]:
         order = [order[i] for i in this_order]
     return order
-
-
-def _qubit_wires(wires):
-    """
-    Return list of Qubits from list of wires.
-
-    Args:
-       wires (list(Bit)): list of bits
-
-    Returns:
-       list(Qubit): returns qubit only wires
-    """
-    from qiskit.circuit import Qubit
-
-    return [bit for bit in wires if isinstance(bit, Qubit)]