Remove Bit.register and Bit.index

[1ucian0]

Summary

Fixes #10744

[qiskit-bot]

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

• @Qiskit/terra-core

[jakelishman]

As it stands, this PR hasn't done the complete job; the register and index arguments from the constructor also need removing, as do most of the actual methods from the class. It'll become almost a completely opaque object. All the private attributes of the object would be deleted as well, since they're no longer necessary.

[coveralls]

Pull Request Test Coverage Report for Build 7262608220

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 9 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.004%) to 87.518%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	1	92.42%
crates/accelerate/src/quantum_circuit/circuit_data.rs	8	90.71%

Totals
Change from base Build 7254198966:	0.004%
Covered Lines:	59141
Relevant Lines:	67576

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💛 - Coveralls

[1ucian0]

Based on how complicated cleaning (see 1ucian0#44) I think it is better to merge this before to warn others the API is changing.

[jakelishman]

This needs a release note about the removal, but given we seem to be going the direction of getting rid of the public components and try to sort out the backend behaviour that we're still accidentally relying on after, the code changes seem complete.

[1ucian0]

reno in 3f16114

[jakelishman]

Thanks!

[jakelishman]

For linking purposes: the work of trying to disentangle the inner _index and _register properties has moved to #11407.