Warning about removal of extras

[1ucian0]

Qiskit 0.44 (with terra 0.25) needs to have an warning about the fact that Qiskit 0.45 (with terra 0.45) will stop having application as extras. This entry is more of a reminder about that.

[qiskit-bot]

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

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 5178356488

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 16 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.06%) to 85.908%

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Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/sabre_swap/mod.rs	1	99.77%
crates/qasm2/src/expr.rs	1	93.76%
crates/qasm2/src/lex.rs	2	91.65%
crates/qasm2/src/parse.rs	12	97.11%

Totals
Change from base Build 5177933484:	0.06%
Covered Lines:	71215
Relevant Lines:	82897

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💛 - Coveralls

[jakelishman]

Let's leave this PR open as a reminder, but in practice we'll effectively need to completely rewrite the release note during the writing of the main prelude, so it might not make too much sense to actually merge it.

We also possibly need to discuss (if we haven't already) what extras we are going to make part of the qiskit package that aren't there yet - qiskit-terra has quite a few, some of which we might want to use this same opportunity to drop (with appropriate warnings).

[mtreinish]

I've included the basic contents here in: Qiskit/qiskit-metapackage#1785 as part of the final metapackage release note. Starting in the next release Qiskit 0.45.0 we'll be doing everything from this repository.