Remove --DRT-oncycle=deprecate option

[dkorpel]

Remove the old "deprecate" mode for cycle handling: #1720

Reduces the size of a void main() {} program. Results from dmd test.d && du test:

	before	after
BUILD=debug	2604 Kb	2588 Kb
BUILD=release	888 Kb	884 Kb

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Testing this PR locally

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[thewilsonator]

Looks fine to me, cc @schveiguy

[dkorpel]

Is there someone who can read the test log and spot the actual error?

[dkorpel]

Looks like it was test_cycles after all, but the output continued after that so it looked like it had to do with code coverage or the gc benchmark on some CIs.

[dkorpel]

Spec PR: dlang/dlang.org#3320

[ljmf00]

Isn't this worth deprecating instead of just removing?

[dkorpel]

Isn't this worth deprecating instead of just removing?

It was a helper for transitioning code that relied on the old faulty cycle checker. It's over 5 years old now, and this is not something worth including in every D program.

[ljmf00]

Isn't this worth deprecating instead of just removing?

It was a helper for transitioning code that relied on the old faulty cycle checker. It's over 5 years old now, and this is not something worth including in every D program.

Ok, if no one is using it makes sense to remove it. We should, at least, leave a notice to remove this in the future and make it completely unrecognized.

[dkorpel]

We should, at least, leave a notice to remove this in the future and make it completely unrecognized.

Done