PHPCS: Enable UnusedFunctionParameter sniff

[obenland]

Proposed changes:

• Removes unused function parameters and their docs.
• Adds a unit test for at_title shortcode to make sure that still works.
• Removes sniff exception.

See #905.

[pfefferle]

won't that result in at least PHP warnings, because the functions are always called with these params, if they are used or not?

[obenland]

Yeah, maybe this needs a different approach

[obenland]

@pfefferle Can you double-check? I think they should just be ignored. I've also not been able to generate a warning in my testing.

[pfefferle]

OK, the shortcode API says:

Three parameters are passed to the shortcode callback function. You can choose to use any number of them including none of them.