Move messages delivery proof verification to pallet (#2189)

* rename messages_proof.rs to proofs.rs

* moved delivery proof verification to the messages pallet

* removed TargetHeaderChain

* cleaning up

* fixed benchmarks compilation

* Update modules/messages/README.md

Co-authored-by: Adrian Catangiu <[email protected]>

* uncommented test and removed printlns

* vec![].into_iter().collect() -> vec![].into()

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Co-authored-by: Adrian Catangiu <[email protected]>