fix(docs): `merge_chains` outdated documentation #6646

Job	Run time
prepare	2s
Check no_std	21s
Check WASM	31s
Build & Test Examples (example_cli)	16s
Build & Test (1.84.0, true, --no-default-features --features miniscript/no-std)	1m 22s
Build & Test Examples (example_bitcoind_rpc_polling)	34s
Rust clippy	23s
Build & Test (1.84.0, true, --all-features)	3m 35s
Build & Test Examples (example_electrum)	55s
Rust fmt	11s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std)	4m 30s
Build & Test Examples (example_esplora)	54s
Build & Test (1.63.0, --all-features)	5m 37s
Build & Test Examples (example_wallet_electrum)	57s
Build & Test Examples (example_wallet_esplora_async)	1m 1s
Build & Test Examples (example_wallet_esplora_blocking)	56s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std)	1m 32s
Build & Test Examples (example_wallet_rpc)	36s
Build & Test (1.75.0, --all-features)	3m 52s
	28m 5s

Provide feedback