Deprecate range-specific step_by

[scottmcm]

Deprecation attributes and test updates only.

Was replaced by an any-iterator version in #41439

Last follow-up (this release) to #42110 (comment)

r? @alexcrichton

[alexcrichton]

Looks great to me, thanks! I think there's one remaining CI error though?

[01:03:21] error: use of deprecated item: replaced by `Iterator::step_by`
[01:03:21] --> /checkout/src/libcollections/../libcollections/tests/vec_deque.rs:513:21
[01:03:21] |
[01:03:21] 513 | let seq = (0..).step_by(2).take(256);
[01:03:21] | ^^^^^^^
[01:03:21] |
[01:03:21] = note: #[deny(deprecated)] implied by #[deny(warnings)]
[01:03:21] note: lint level defined here
[01:03:21] --> /checkout/src/libcollections/../libcollections/tests/lib.rs:11:9
[01:03:21] |
[01:03:21] 11 | #![deny(warnings)]
[01:03:21] | ^^^^^^^^
[01:03:21] [01:03:21] error: aborting due to previous error(s)
[01:03:21] [01:03:21] error: Could not compile `collections`.

[scottmcm]

Oops, I missed a step. Closing temporarily; will re-open after #42315.

[scottmcm]

Reopening as #42315 has landed, allowing some more tests to be moved over to Iterator::step_by.

[alexcrichton]

@bors: r+

Thanks @scottmcm!

[bors]

📌 Commit 15dff84 has been approved by alexcrichton

[Mark-Simulacrum]

@bors rollup