Revert "Add advance_by and advance_back_by"

[ecstatic-morse]

r? @ghost

[rust-highfive]

r? @Mark-Simulacrum

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[ecstatic-morse]

@bors try
@rust-timer queue

[rust-timer]

Awaiting bors try build completion

[bors]

⌛ Trying commit e16d17a with merge 66905b979037ebdafdb00186e8d15dc1f358750d...

[bors]

☀️ Try build successful - checks-actions, checks-azure
Build commit: 66905b979037ebdafdb00186e8d15dc1f358750d (66905b979037ebdafdb00186e8d15dc1f358750d)

[rust-timer]

Queued 66905b979037ebdafdb00186e8d15dc1f358750d with parent a1dfd24, future comparison URL.

[rust-timer]

Finished benchmarking try commit (66905b979037ebdafdb00186e8d15dc1f358750d): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never