doc: Update comment describing CheckInputs in validation.cpp #16781

In the Bitcoin Core PR review club @jnewbery noted that the comment describing the CheckInputs() function is no longer accurate.

13:10 < jnewbery> Note that the CheckInputs function is slightly confusingly named (and the comment above is incorrect in parts) 13:11 < jnewbery> The comment says "Check whether all inputs of this transaction are valid (no double spends, scripts & sigs, amounts) 13:11 < jnewbery> historically, that was true (it'd check amounts and doublespends). Now it only checks scripts and sigs.

CheckInputs() no longer checks amounts and double spends and so I have deleted double spends and amounts from the comment. @jnewbery also noted that CheckInputs() is confusingly named and so the function name should be replaced.

If there is an obvious function name replacement then perhaps replacing the function name should be included in this PR. For now I thought it best to just change the comment and open an issue on what this function name replacement should be. I don't know if there is an obvious replacement. If that is a suboptimal approach please comment below.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #16658 ([WIP] validation: Rename CheckInputs to CheckInputScripts by jnewbery)

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.

Closing this as @jnewbery already opened a PR to do this (#16658), apologies.

(Testing the GitHub API to pick up reviews, ignore this.)