chore: remove unnecessary black_box in criterion #650

Job	Run time
lint	47s
msrv-check	49s
tests	9m 2s
compat-integration-test-walltime (codspeed-criterion-compat)	10m 49s
compat-integration-test-walltime (codspeed-divan-compat-examples)	4m 37s
compat-integration-test-instrumentation (-p codspeed-bencher-compat)	1m 37s
compat-integration-test-instrumentation (-p codspeed-divan-compat-examples)	2m 32s
compat-integration-test-instrumentation (-p codspeed-divan-compat)	1m 42s
compat-integration-test-instrumentation (-p codspeed)	1m 41s
compat-integration-test-walltime (codspeed-divan-compat)	3m 49s
compat-integration-test-instrumentation (--features async_futures -p codspeed-criterion-compat)	2m 5s
check	6s
	39m 36s

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