Warn if no violations were produced in a disabled region

[jpsim]

Maybe SwiftLint should warn if a disable command doesn't actually silence a violation?

Due to SwiftLint's architecture, we already detect these violations, we just filter them out (silence them) if they happen to be in a disabled region before passing it back to the linter.

So it shouldn't be too hard to do this.

[heidiproske]

❤ yes please! I recently did this (manually) and was able to remove a bunch of unnecessary disable flags. (The project had been refactored and Linting had been disabled for a while so things became out of date.)

[marcelofabri]

Closed in #1740.