Simplify tx queue, remove transaction chains support #4812

Job	Run time
fmt	11s
cargo-deny (advisories)	41s
build (gcc, current)	52m 32s
rust-check-git-rev-deps	15s
cargo-deny (bans licenses sources)	43s
cackle	1m 17s
build (gcc, current, --check-test-tx-meta)	52m 38s
build (gcc, next)	52m 49s
build (gcc, next, --check-test-tx-meta)	53m 32s
build (clang, current)	42m 42s
build (clang, current, --check-test-tx-meta)	46m 4s
build (clang, next)	43m 33s
build (clang, next, --check-test-tx-meta)	47m 33s
complete	1s
	6h 34m 31s

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