Revert "Single-pass ASCII lower/upper case conversion" for benchmark

[JonathanBrouwer]

PR exists only to do a perf run of #160480

• I did not use an LLM to create a change in this PR.
• I used an LLM to create a change in this PR, and I have explained below how it was used.

[JonathanBrouwer]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 792df37 (792df37c7166d19d203a052924afc5bcac1368db)
Base parent: 65bcac4 (65bcac45b3d8a8b2126e5cc844cf6fff5795d32a)

[rust-timer]

Finished benchmarking commit (792df37): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

@bors rollup=never rustc-perf
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.8%	[-1.6%, -0.3%]	7
Improvements ✅ (secondary)	-0.8%	[-1.6%, -0.5%]	5
All ❌✅ (primary)	-0.6%	[-1.6%, 0.7%]	8

Max RSS (memory usage)

Results (primary -3.5%, secondary -0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.5%	[0.4%, 0.8%]	4
Improvements ✅ (primary)	-3.5%	[-3.5%, -3.5%]	1
Improvements ✅ (secondary)	-1.1%	[-1.7%, -0.5%]	2
All ❌✅ (primary)	-3.5%	[-3.5%, -3.5%]	1

Cycles

Results (secondary 0.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.1%	[0.5%, 2.8%]	10
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.7%	[-1.1%, -0.4%]	7
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.6%, secondary -1.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.6%, 0.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-2.5%, -0.1%]	18
Improvements ✅ (secondary)	-1.9%	[-1.9%, -1.9%]	1
All ❌✅ (primary)	-0.6%	[-2.5%, 0.6%]	19

Bootstrap: 458.664s -> 461.289s (0.57%)
Artifact size: 398.60 MiB -> 398.63 MiB (0.01%)