MOVEONLY: Move helper functions from rpcwallet to wallet/rpc/util #23640

This is part one of multiple to split up rpcwallet.cpp into smaller, more logical units.

See #23622 for context and overall plan. I'll open PRs in stages to hopefully minimise conflicts.

Can be reviewed with --color-moved=dimmed-zebra

The end goal can be seen here: https://github.com/meshcollider/bitcoin/tree/202111_split_walletrpc

nice, ACK ff945e553affbb7e25da1257a0dd47e413ec5164 🐰

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nice, ACK ff945e553affbb7e25da1257a0dd47e413ec5164 🐰
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ACK ff945e553affbb7e25da1257a0dd47e413ec5164

This PR along with its original agenda also:

1. Removes static and static inline keywords from the functions that were moved.
2. Removes unnecessary imports and declarations of headers and classes. The removed headers and classes were either unused or were imported along with other imported files.

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The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #23497 (Add src/node/ and src/wallet/ code to node:: and wallet:: namespaces by ryanofsky)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.