convert C-style (void) parameter lists to C++ style () #14214

In C, an empty parameter list, (), means the function takes any arguments, and (void) means the function does not take any parameters. In C++, an empty parameter list means the function does not take any parameters.

So, C++ still supports (void) parameter lists with the same semantics, why change to ()?

1. removing the redundant void improves signal-to-noise ratio of the code
2. using (void) exposes a rare inconsistency in that a template taking a template (T) parameter list, cannot be instantiated with T=void

utACK https://github.com/bitcoin/bitcoin/commit/3ccfa34b32b7ed9d7bef05baa36827b4b262197e

Interesting. utACK 3ccfa34.

utACK 3ccfa34b32b7ed9d7bef05baa36827b4b262197e

Nice cleanup!

<!--e57a25ab6845829454e8d69fc972939a-->Note to reviewers: This pull request conflicts with the following ones:

• #14267 (gui: Mark Qt methods as override where appropriate by Empact)
• #14224 (Add -fsanitize=integer Travis job. Document intentional and unintentional unsigned integer overflows (wraparounds) using annotations. by practicalswift)
• #13864 (validation: Document where we are intentionally ignoring bool return values from validation related functions by practicalswift)

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.

I compiled with clang and the code change doesn't change a single bit of the bitcoind binary. (Didn't check test_bitcoin and bitcoin-qt)

utACK 3ccfa34

utACK 3ccfa34

Nice cleanup indeed.

NL.25: Don’t use void as an argument type "It’s verbose and only needed where C compatibility matters."

As a nit, maybe replace the void () instances with void() in scheduler.