Remove fake backends based on BackendV1 and related tools (Qiskit#13805)

* Remove FakeBackend, FakeQasmBackend, FakePulseBackend, subclasses, any tests that checked V1 functionality, mitigators (independent removal). Update rest of unit tests to use GenericBackendV2

* Remove FakeBackend references from docs (these classes will be removed in 2.0 so no alternative is provided)

* Fix lint and apply desperate measures until better measures are found (visual tests).

* Add renos

* Fix scheduling tests, lints and docs issue.

* Apply suggestions from Eli's code review

Co-authored-by: Eli Arbel <[email protected]>

* Migrate relevant fake backend tests to test_generic_backend_v2.py, remove non-relevant tests

* Fix merge conflict, apply review suggestions reno

* Fix reno typo

Co-authored-by: Eli Arbel <[email protected]>

---------

Co-authored-by: Eli Arbel <[email protected]>

Author: ElePT

qiskit/compiler/transpiler.py

@@ -201,7 +201,7 @@ def transpile(  # pylint: disable=too-many-return-statements
             If unit is omitted, the default is 'dt', which is a sample time depending on backend.
             If the time unit is 'dt', the duration must be an integer.
         dt: Backend sample time (resolution) in seconds.
-            If ``None`` (default), ``backend.configuration().dt`` is used.
+            If ``None`` (default), ``backend.dt`` is used.
         approximation_degree (float): heuristic dial used for circuit approximation
             (1.0=no approximation, 0.0=maximal approximation)
         timing_constraints: An optional control hardware restriction on instruction time resolution.

qiskit/providers/fake_provider/__init__.py

@@ -65,42 +65,5 @@
 
     GenericBackendV2
 
-V1 Fake Backends (Legacy interface)
-===================================
-
-.. autosummary::
-    :toctree: ../stubs/
-
-    FakeOpenPulse2Q
-    FakeOpenPulse3Q
-    Fake1Q
-    Fake5QV1
-    Fake20QV1
-    Fake7QPulseV1
-    Fake27QPulseV1
-    Fake127QPulseV1
-
-Fake Backend Base Classes
-=========================
-
-The V1 fake backends are based on a set of base classes:
-
-.. currentmodule:: qiskit.providers.fake_provider
-.. autoclass:: FakeBackend
-.. autoclass:: FakeQasmBackend
-.. autoclass:: FakePulseBackend
 """
-
-# Base classes for fake backends
-from .fake_backend import FakeBackend
-from .fake_qasm_backend import FakeQasmBackend
-from .fake_pulse_backend import FakePulseBackend
-
-# Special fake backends for special testing purposes
-from .fake_openpulse_2q import FakeOpenPulse2Q
-from .fake_openpulse_3q import FakeOpenPulse3Q
-from .fake_1q import Fake1Q
-
-# Generic fake backends
-from .backends_v1 import Fake5QV1, Fake20QV1, Fake7QPulseV1, Fake27QPulseV1, Fake127QPulseV1
 from .generic_backend_v2 import GenericBackendV2