refactor(wallet): cleanup and remove unused code in create_tx #6470

Job	Run time
prepare	3s
Build and test (stable, true, --no-default-features --features miniscript/no-std)	2m 7s
Build and test (stable, true, --all-features)	4m 0s
Build and test (1.63.0, --no-default-features --features miniscript/no-std)	3m 13s
Build & Test Examples (example_cli)	23s
Build and test (1.63.0, --all-features)	5m 18s
Check no_std	11s
Build & Test Examples (example_bitcoind_rpc_polling)	46s
Build & Test Examples (example_electrum)	41s
Build & Test Examples (example_esplora)	48s
Check WASM	42s
Rust fmt	3s
Build & Test Examples (example_wallet_electrum)	41s
Build & Test Examples (example_wallet_esplora_async)	58s
Build & Test Examples (example_wallet_esplora_blocking)	47s
Build & Test Examples (example_wallet_rpc)	28s
clippy_check	1m 6s
	22m 15s

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