Transpiler won't remove Gate->Inverse pairs when basis_gates is None

Reported by @ewoutvandenberg , unless a basis is specified, the transpiler does not remove pairs of gate-inverse gate. e.g.

>>> qc = qk.QuantumCircuit(1)
>>> qc.s(0)
>>> qc.sdg(0)
>>> print(qc)
        ┌───┐┌─────┐
q_0: |0>┤ S ├┤ Sdg ├
        └───┘└─────┘
>>> print(qk.transpile(qc))
        ┌───┐┌─────┐
q_0: |0>┤ S ├┤ Sdg ├
        └───┘└─────┘
>>> print(qk.transpile(qc, basis_gates=['u3']))

q_0: |0>

[kdk]

There is. Without a backend, the transpiler should be able to (and presently does) apply backend-independent, logical optimizations.

[1ucian0]

This seems related to https://github.com/Qiskit/qiskit-terra/issues/6576 and https://github.com/Qiskit/qiskit-terra/issues/7016.

~I think InverseCancellation should just replace CXCancellation in level 1.~ because https://github.com/Qiskit/qiskit-terra/issues/7413