Remove DAGNode deprecations

[enavarro51]

Summary

Removes DAGNode deprecations

Details and comments

Since 0.20.0 has been released and the 3 months have passed, this PR removes the deprecations to DAGNode that were added as part of #6567.

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[coveralls]

Pull Request Test Coverage Report for Build 2261384756

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 84.349%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/dagcircuit/dagnode.py	1	89.39%

Totals
Change from base Build 2261332291:	0.02%
Covered Lines:	54463
Relevant Lines:	64569

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💛 - Coveralls

[kdk]

Thanks @enavarro51 , it looks like there's a section in the tutorial https://github.com/Qiskit/qiskit-tutorials/blob/721d67ac97e8f0ca3b9b4156cc35a9a777363d12/tutorials/circuits_advanced/04_transpiler_passes_and_passmanager.ipynb that still uses the deprecated node.condition form and is leading to the failure at https://dev.azure.com/qiskit-ci/qiskit-terra/_build/results?buildId=35731&view=logs&j=b32a9d47-7bd3-5443-5e7c-fab46a446055&t=186ae8ed-dea6-5bc5-f4e3-12f54632f4a9&l=60 . That would need to be updated before this PR can merge.

[kdk]

Thanks @enavarro51 , this looks good to me. Can you add a "removal" release note?

[enavarro51]

Actually as I looked at this, should we be leaving the name getter and setter? I thought we were going to still allow node.name. Thanks.

[enavarro51]

@kdk Ok. Release note done and I put the name setter and getter back.

[enavarro51]

@kdk. NVM. Just realized name getter and setter were now in DAGOpNode. Should be all good now.

[kdk]

Thanks @enavarro51 , this looks good to me!

[jakelishman]

There was a seemingly bad-luck test failure on this on Windows/Python3.7, so I've restarted that, and it should go through now.