Remove workarounds for qiskit-aer 0.13.0

+ Unpin qiskit-aer extra requirement now that 0.13.1 has been released
  and we do not have to worry about
Qiskit/qiskit-aer#1985
+ Remove workaround in test for
  Qiskit/qiskit-aer#1975

Note that the tests will not pass with 0.13.0 because the workaround was
removed, but the workaround was for an Aer bug so we don't reflect it as
an incomapitibility with qiskit-experiments.

requirements-extras.txt

@@ -1,5 +1,5 @@
 qiskit-ibm-provider>=0.6.1 # for submitting experiments to backends through the IBM provider
 cvxpy>=1.3.2 # for tomography
 scikit-learn # for discriminators
-qiskit-aer>=0.11.0,<=0.12.2 # temporary version pin until 0.13.1 release
+qiskit-aer>=0.11.0
 qiskit_dynamics>=0.4.0 # for the PulseBackend

test/library/tomography/tomo_utils.py

@@ -87,9 +87,7 @@ def readout_noise_model(num_qubits, seed=None):
     p1g0s = 0.15 * rng.random(num_qubits)
     p0g1s = 0.3 * rng.random(num_qubits)
     amats = np.stack([[1 - p1g0s, p1g0s], [p0g1s, 1 - p0g1s]]).T
-    # Set `basis_gates` so that reset is included.
-    # See https://github.com/Qiskit/qiskit-aer/issues/1975
-    noise_model = NoiseModel(basis_gates=["id", "rz", "sx", "cx", "reset"])
+    noise_model = NoiseModel()
     for i, amat in enumerate(amats):
         noise_model.add_readout_error(amat.T, [i])
     return noise_model