zcash_client_backend: Remove deprecated and duplicative wallet APIs. #5976

Job	Run time
Latest build on ubuntu-latest	2m 4s
Latest build on windows-latest	4m 14s
Build target wasm32-wasi	52s
Latest build on macOS-latest	1m 50s
Bitrot check	1m 30s
Check ZFuture build on Linux	22s
Check ZFuture build on macOS	35s
Clippy (MSRV)	1m 15s
Check ZFuture build on Windows	1m 37s
Test on Linux	8m 57s
Test Orchard on Linux	10m 45s
Clippy (beta)	13s
Test NU6 on Linux	8m 50s
Test on macOS	12m 14s
Code coverage	56m 25s
Test Orchard on macOS	14m 32s
Test on Windows	18m 10s
Intra-doc links	2m 11s
Test Orchard on Windows	21m 24s
Test NU6 on Windows	18m 7s
Rustfmt	16s
protobuf consistency	1m 8s
UUID validity	5s
	3h 7m 36s

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