Migrate pallet-xcm-benchmarks/generic to benchmarking v2 syntax #14942

Job	Run time
check-workspace	17s
check-dependency-rules	9s
check-fail-ci	12s
check-markdown	13s
check-readme	3m 35s
preflight / preflight	44s
preflight / ci-versions	55s
check-rust-feature-propagation	2m 3s
check-toml-format	1m 0s
check-umbrella	2m 22s
fmt	1m 4s
test-rust-features	2m 5s
All quick checks passed	1s
	14m 40s

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