Delete github-action-benchmark repo directory

[mothran]

Hopefully fixes issues with the benchmark-data-repository directory existing between workflow runs:
https://github.com/risc0/risc0/actions/runs/4692258699/jobs/8317753772

[github-actions]

Benchmark for Linux-cuda d3ed01b

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Test	Base	PR	%
fib/100/proof	850.1±63.32ms	837.7±43.99ms	-1.46%
fib/100/run	335.8±7.20ms	335.5±10.78ms	-0.09%
fib/200/proof	895.8±37.63ms	847.2±48.64ms	-5.43%
fib/200/run	345.3±6.38ms	338.0±8.14ms	-2.11%

Benchmark for Linux-default d3ed01b

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Test	Base	PR	%
fib/100/proof	2.3±0.02s	2.3±0.01s	0.00%
fib/100/run	332.6±7.39ms	320.3±1.39ms	-3.70%
fib/200/proof	2.3±0.01s	2.3±0.01s	0.00%
fib/200/run	330.2±2.04ms	328.6±5.71ms	-0.48%

Benchmark for macOS-default d3ed01b

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Test	Base	PR	%
fib/100/proof	1601.7±13.60ms	1594.1±7.14ms	-0.47%
fib/100/run	112.9±0.69ms	111.8±0.47ms	-0.97%
fib/200/proof	1610.4±26.38ms	1606.8±25.69ms	-0.22%
fib/200/run	114.8±0.65ms	114.0±0.62ms	-0.70%

Benchmark for macOS-metal d3ed01b

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Test	Base	PR	%
fib/100/proof	465.0±2.36ms	464.8±5.40ms	-0.04%
fib/100/run	113.9±0.33ms	113.8±0.44ms	-0.09%
fib/200/proof	467.5±4.66ms	466.6±4.83ms	-0.19%
fib/200/run	115.9±0.31ms	115.7±0.59ms	-0.17%