Remove patching of SwapGate.__new__ from Sabre test (#11012)

This made sense as a way of tracking the progress of Sabre back when our
implementation was pure-Python and generated the swaps on-the-fly, but
ever since it moved to Rust, the infinite loop would have happened
before any swaps were constructed at all.

With the move to singleton gates, this test can cause problems; the
restoration after the patching can cause issues with the
singleton-return apparatus.

test/python/transpiler/test_sabre_swap.py

@@ -230,18 +230,9 @@ def test_no_infinite_loop(self, method):
         coupling_map = CouplingMap.from_line(qc.num_qubits)
         routing_pass = PassManager(SabreSwap(coupling_map, method))
 
-        n_swap_gates = 0
-
-        def leak_number_of_swaps(cls, *args, **kwargs):
-            nonlocal n_swap_gates
-            n_swap_gates += 1
-            if n_swap_gates > 1_000:
-                raise Exception("SabreSwap seems to be stuck in a loop")
-            # pylint: disable=bad-super-call
-            return super(SwapGate, cls).__new__(cls, *args, **kwargs)
-
-        with unittest.mock.patch.object(SwapGate, "__new__", leak_number_of_swaps):
-            routed = routing_pass.run(qc)
+        # Since all the logic happens in Rust space these days, the best we'll really see here is
+        # the test hanging.
+        routed = routing_pass.run(qc)
 
         routed_ops = routed.count_ops()
         del routed_ops["swap"]