Add dummy starknet_getStorageProof, remove unused Serialize

[FabijanC]

Usage related changes

• Part of JSON-RPC API 0.8.0 adaptation #613

Development related changes

• The corresponding type for starknet_getStorageProof is set to be a dummy serde_json::Value since that case should never happen.
• The input type for starknet_getStorageProof to serve at least as a structure verifier for users wanting to test interaction with this endpoint.
• Remove unused Serialize derivations on RPC input structs.
• Define is_forwardable_to_origin to return true for starknet_getStorageProof in case it's called with an old origin block.

Checklist:

• Checked out the contribution guidelines
• Applied formatting - ./scripts/format.sh
• No linter errors - ./scripts/clippy_check.sh
• No unused dependencies - ./scripts/check_unused_deps.sh
• No spelling errors - ./scripts/check_spelling.sh
• Performed code self-review
• Rebased to the latest commit of the target branch (or merged it into my branch)
  • Once you make the PR reviewable, please avoid force-pushing
• Updated the docs if needed - ./website/README.md
• Linked the issues resolvable by this PR - linking info
• Updated the tests if needed; all passing - execution info