replace bootstrap-self-test feature flag with cfg(test)

[onur-ozkan]

This makes it in more rusty way.

[rustbot]

r? @albertlarsan68

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[rustbot]

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

[clubby789]

@bors r+

[bors]

📌 Commit 485c20d has been approved by clubby789

It is now in the queue for this repository.

[bors]

⌛ Testing commit 485c20d with merge ceb0441...

[bors]

☀️ Test successful - checks-actions
Approved by: clubby789
Pushing ceb0441 to master...

[rust-timer]

Finished benchmarking commit (ceb0441): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary -2.8%, secondary 0.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-2.8%	[-2.8%, -2.8%]	1
Improvements ✅ (secondary)	-1.7%	[-1.7%, -1.7%]	1
All ❌✅ (primary)	-2.8%	[-2.8%, -2.8%]	1

Cycles

Results (primary 2.0%, secondary -2.5%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.5%	[-2.5%, -2.5%]	1
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	1

Binary size

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

Bootstrap: 763.352s -> 762.432s (-0.12%)
Artifact size: 325.46 MiB -> 325.44 MiB (-0.01%)