Do not use `?` at the end of boolean function

In clarity functions, the question mark is used to indicate optional or wrapped results, e.g. `to-consensus-buff?`

There should be code guidelines that suggest to not use question mark for boolean results, example [`has-duplicate-chars?`](https://github.com/hirosystems/recipes/blob/f0815d99ac9e812b3966aa1af835cc455039c2f3/recipes/check-for-duplicates.mdx)