Remove dupe storage item if we get one back, to be compatible with Smoldot + legacy RPCs #4519

Job	Run time
Check unused dependencies	35s
Cargo fmt	20s
Cargo clippy (WASM)	1m 5s
Cargo check (WASM)	1m 43s
Cargo clippy	4m 56s
Cargo check	6m 20s
Check documentation and run doc tests	5m 29s
Test (no_std)	2m 21s
Test (Native)	9m 32s
Test (Light Client)	3m 8s
Test (Unstable Backend)	8m 45s
Test (WASM)	6m 12s
	50m 26s

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