Migrate pallet-democracy benchmarks to benchmark v2 syntax #14155

Job	Run time
check-dependency-rules	9s
check-fail-ci	15s
check-markdown	15s
check-readme	4m 9s
check-workspace	39s
preflight / preflight	44s
preflight / ci-versions	1m 5s
check-rust-feature-propagation	2m 17s
fmt	1m 26s
check-toml-format	1m 23s
check-umbrella	2m 41s
test-rust-features	2m 25s
All quick checks passed	1s
	17m 29s

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