Omit QuantumCircuit as a parameter when drawing ControlFlowOps. (#7345)

Most ControlFlowOps have at least one param of type QuantumCircuit
which qiskit.visualization.utils.get_param_str will attempt to
stringify and display as an instruction parameter. This largely
doesn't work, since the circuit's string will contain newlines, so
instead draw ControlFlowOps with only their name.

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>

qiskit/visualization/utils.py

@@ -25,6 +25,7 @@ from qiskit.circuit import (
     Gate,
     Instruction,
     Measure,
+    ControlFlowOp,
 )
 from qiskit.circuit.library import PauliEvolutionGate
 from qiskit.circuit.tools import pi_check
@@ -129,6 +130,9 @@ def get_param_str(op, drawer, ndigits=3):
     if not hasattr(op, "params") or any(isinstance(param, np.ndarray) for param in op.params):
         return ""
 
+    if isinstance(op, ControlFlowOp):
+        return ""
+
     if isinstance(op, Delay):
         param_list = [f"{op.params[0]}[{op.unit}]"]
     else: