chore: specify `yarn` as package manager and remove unused dependency #534

Job	Run time
check_react_and_ujs (2.7)	30s
test (npm, npm, 2.7, base)	1m 1s
test (npm, npm, 2.7, shakapacker)	1m 55s
test (npm, npm, 2.7, sprockets_3)	1m 19s
test (npm, npm, 2.7, sprockets_4)	1m 26s
test (yarn_classic, yarn, 2.7, base)	1m 1s
test (yarn_classic, yarn, 2.7, shakapacker)	2m 1s
test (yarn_classic, yarn, 2.7, sprockets_3)	1m 21s
test (yarn_classic, yarn, 2.7, sprockets_4)	1m 24s
test (pnpm, pnpm, 2.7, base)	1m 6s
test (pnpm, pnpm, 2.7, shakapacker)	1m 58s
test (pnpm, pnpm, 2.7, sprockets_3)	1m 16s
test (pnpm, pnpm, 2.7, sprockets_4)	1m 21s
test (bun, bun, 2.7, base)	52s
test (bun, bun, 2.7, shakapacker)	1m 39s
test (bun, bun, 2.7, sprockets_3)	1m 41s
test (bun, bun, 2.7, sprockets_4)	1m 18s
	23m 9s

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