Remove deprecated features from >3 months ago and TODOs

[jyu00]

What is the expected feature or enhancement?

Many features were deprecated in 0.7 release and can be removed now. In light of this issue, the TODOs in the code should be reviewed and actions taken accordingly.

Acceptance criteria

• Remove features that had sufficient deprecation period per Qiskit's deprecation policy
• Review/fix all TODOs

[merav-aharoni]

@kt474 - deprecated code for which versions can be removed?

[kt474]

@kt474 - deprecated code for which versions can be removed?

I believe all the deprecated code from 0.7 has been removed in #797 but there are plenty of TODO's in the codebase that can be addressed

[merav-aharoni]

I looked at the deprecation message in session.py:

        if "backend" in options:
            issue_deprecation_msg(
                "'backend' is no longer a supported option within a session",
                "0.9",
                "Instead, specify a backend when creating a Session instance.",
                3,
            )

I tried to raise an error if backend is defined in options, instead of the deprecation message. This does not work, because session.run itself adds self._backend to its options. So if session.run is called more than once, it will have backend inside options.
What should the specification be here? I think that we should remove backend from options in all levels and add it as an extra parameter on all run levels, since in QiskitRuntimeService.run we extract it from options anyway. Having backend both as a class member and in options is confusing. @kt474 , @jyu00 - I'd appreciate your inputs.

[kt474]

Yes, it is a bit confusing - originally, I believe we wanted all options passed into session.run() to be honored, but in terms of backend, it never worked because sessions don't support cross multiple backends. This deprecation message was meant to just inform users not to pass in a backend in the options and the doc strings say the same thing. I'm ok with just leaving this deprecation message for now, as I don't believe any users are doing this anymore anyway.

I agree that ideally, backend is not an option, but it would be a relatively big change unrelated to this original issue

[jyu00]

We can just make a copy of the input options before adding backend to it. We really shouldn't be modifying a user's variable to begin with anyway.

We can remove/privatize both session.run() and service.run() once everything becomes primitives only (i.e. no more custom programs).

[kt474]

I believe #1093 handles the last deprecation warning we can remove, after it's in we can close this issue

Update 11/08 : we've handled all deprecation warnings but there are still plenty TODOs it code base

[jyu00]

closing this, but as part of the release process we should always check if there are deprecated features that can be removed.