zcash_client_backend: Remove deprecated and duplicative wallet APIs. #5965

Job	Run time
Bitrot check	1m 31s
Build target wasm32-wasi	56s
Latest build on ubuntu-latest	1m 59s
Latest build on windows-latest	4m 56s
Check ZFuture build on Linux	23s
Latest build on macOS-latest	2m 29s
Clippy (MSRV)	1m 20s
Check ZFuture build on macOS	35s
Check ZFuture build on Windows	1m 37s
Clippy (beta)	14s
Code coverage	10m 18s
Intra-doc links	2m 13s
Rustfmt	13s
protobuf consistency	1m 8s
UUID validity	7s
Test on Linux	4m 48s
Test Orchard on Linux	4m 48s
Test NU6 on Linux	4m 41s
Test on macOS	5m 4s
Test Orchard on macOS	5m 2s
Test on Windows	4m 53s
Test Orchard on Windows	3m 34s
Test NU6 on Windows	3m 53s
	1h 6m 42s

Provide feedback