Deprecation 0.45 extensions

[henryzou50]

Summary

Remove feature deprecated in 0.45 in qiskit/extensions

Details and comments

The files removed are:

• 'qiskit/extensions/exceptions.py'
• 'qiskit/extensions/simulator/snapshot.py'

I was unsure whatever to remove 'qiskit/extensions/simulator/init.py' as now it includes no code. If this is removed, we could also remove the directory qiskit/extensions/simulator/

[qiskit-bot]

One or more of the the following people are requested to review this:

• @Qiskit/terra-core

[Cryoris]

This is already done in #11488, but merging is currently blocked as we're waiting for Aer 0.13.2 to release, which removes their usage of qiskit.extensions 🙂

[mtreinish]

Thanks for doing this @henryzou50 but since #11488 merged this has been superseded. I'm going to close this as it was already completed by @Cryoris in #11488. If I'm missing something please feel free to re-open this though.