Clean up submodule checkout scripts

[ehuss]

This is just some small cleanup:

• Removed unused CACHE_DIR stuff
• Removed duplicate fetch_github_commit_archive function which is no longer used
• Combined init_repo.sh and checkout-submodules.sh, as checkout-submodules.sh was doing nothing but calling init_repo.sh

[rust-highfive]

r? @Mark-Simulacrum

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[Mark-Simulacrum]

@bors r+ rollup=iffy

[bors]

📌 Commit 124557c has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 124557c with merge 495b216...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 495b216 to master...

[rust-timer]

Finished benchmarking commit (495b216): comparison url.

Instruction count

• Primary benchmarks: 😿 relevant regressions found
• Secondary benchmarks: 😿 relevant regressions found

	mean1	max	count2
Regressions 😿 (primary)	1.3%	1.4%	2
Regressions 😿 (secondary)	1.7%	3.3%	12
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	1.3%	1.4%	2

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results

• Primary benchmarks: 😿 relevant regressions found
• Secondary benchmarks: 🎉 relevant improvement found

	mean1	max	count2
Regressions 😿 (primary)	2.7%	3.6%	2
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-2.9%	-2.9%	1
All 😿🎉 (primary)	2.7%	3.6%	2

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩²

2. number of relevant changes ↩ ↩²

[Mark-Simulacrum]

Clearly not an actual regression, or at least not one we can do anything about; this wouldn't have affected generated code at all in my expectation.