validation: remove unused using directives

[Crypt-iQ]

I noticed the following were unused from the node namespace in validation.cpp:

• BLOCKFILE_CHUNK_SIZE
• nPruneTarget
• OpenBlockFile
• UNDOFILE_CHUNK_SIZE

I am not sure if maybe there is some reason these are still defined here in which case I'll close this

[DrahtBot]

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

Conflicts

No conflicts as of last run.

[Crypt-iQ]

I noticed there is another one in src/rpc/transaction.cpp for ReadBlockFromDisk

[maflcko]

not sure if this is worth it. If it is, maybe a iwyu/linter/tidy check would be better?

[Crypt-iQ]

I think an automated check would be better than this, but I wouldn't want to add something that rarely catches anything (I think an unused using directive would be kind of rare?). Maybe it's better to let somebody remove these as part of a larger validation PR

[maflcko]

We already run clang-tidy, so there is no additional cost of enabling https://clang.llvm.org/extra/clang-tidy/checks/misc/unused-using-decls.html

The question is: Is it worth it?

If the clang-tidy check helps to avoid:

• pr flood to "fix" this issue
• review comments to suggest to "fix" this issue
• wasted review on re-ACKs if the style comment is addressed

I'd say it is worth it.

(Surely it is frustrating to open a pull request and see a red CI 6 minutes later, but if a pull request author isn't willing to put up 6 minutes of their time, maybe they shouldn't open a pull request in the first place to ask others to spend time on it.)