Remove initial layout default from level 1

Now that vf2 layout has limited noise awareness and multiple trials it
no longer will be defaulting to the worst qubits like it was with only a
single sample when vf2++ is used. This commit removes the implicit
trivial layout attempt as it's no longer needed.

qiskit/transpiler/preset_passmanagers/level1.py

@@ -110,24 +110,6 @@ def level_1_pass_manager(pass_manager_config: PassManagerConfig) -> PassManager:
     def _choose_layout_condition(property_set):
         return not property_set["layout"]
 
-    def _trivial_not_perfect(property_set):
-        # Verify that a trivial layout is perfect. If trivial_layout_score > 0
-        # the layout is not perfect. The layout is unconditionally set by trivial
-        # layout so we need to clear it before contuing.
-        if property_set["trivial_layout_score"] is not None:
-            if property_set["trivial_layout_score"] != 0:
-                property_set["layout"]._wrapped = None
-                return True
-        warnings.warn(
-            "The current implicit default of using a trivial layout if it's a "
-            "perfect layout will change in a future release, if you're "
-            "depending on this behavior it is better to explicit set "
-            "layout_method='trivial' when calling transpile()",
-            FutureWarning,
-            stacklevel=4,  # stack_level=4 to target caller of transpile()
-        )
-        return False
-
     def _vf2_match_not_found(property_set):
         # If a layout hasn't been set by the time we run vf2 layout we need to
         # run layout
@@ -147,15 +129,6 @@ def _vf2_match_not_found(property_set):
         vf2_seed = -1
 
     _choose_layout_0 = (
-        []
-        if pass_manager_config.layout_method
-        else [
-            TrivialLayout(coupling_map),
-            Layout2qDistance(coupling_map, property_name="trivial_layout_score"),
-        ]
-    )
-
-    _choose_layout_1 = (
         []
         if pass_manager_config.layout_method
         else VF2Layout(
@@ -328,7 +301,6 @@ def _contains_delay(property_set):
         pm1.append(_unroll3q)
         pm1.append(_given_layout)
         pm1.append(_choose_layout_0, condition=_choose_layout_condition)
-        pm1.append(_choose_layout_1, condition=_trivial_not_perfect)
         pm1.append(_improve_layout, condition=_vf2_match_not_found)
         pm1.append(_embed)
         pm1.append(_swap_check)

releasenotes/notes/vf2layout-preset-passmanager-db46513a24e79aa9.yaml

@@ -31,18 +31,13 @@ upgrade:
     unlike with optimization level 2 and 3 a trivial layout is attempted
     prior to running :class:`~qiskit.transpiler.passes.VF2Layout` and if
     it's a perfect mapping this will be used instead.
-deprecations:
   - |
     For the preset pass manager for optimization level 1 (when calling
     :func:`~qiskit.compiler.transpile` with ``optimization_level=1`` or
     no ``optimization_level`` argument set) as generated by
     :func:`~qiskit.transpiler.preset_passmanagers.level_1_pass_manager` the
     implict default of running ::class:`~qiskit.transpiler.passes.TrivialLayout`
-    and using the trivial layout if it's a perfect match is deprecated
-    and this behavior will change in a future release. A ``FutureWarning`` is
-    now emitted whenever a trivial layout is used by default with optimization
-    level 1. This means that :func:`~qiskit.compiler.transpile` by default may
-    emit a ``FutureWarning`` if it picks a trivial layout as a result of this
-    current behavior. If this default towards a trivial layout is desired you
+    and using the trivial layout if it's a perfect match is no longer the
+    behavior. If this default towards a trivial layout is desired you
     can explicitly request it when transpiling by specifying
     ``layout_method="trivial"`` when calling :func:`~qiskit.compiler.transpile`.