Ban Unused Ignore

Warns unused ignore directives.

We sometimes have to suppress and ignore lint errors for some reasons and we can do so using ignore directives.

In some cases, however, like after refactoring, we may end up having ignore directives that are no longer necessary. Such superfluous ignore directives are likely to confuse future code readers, and to make matters worse, might hide future lint errors unintentionally. To prevent such situations, this rule detects unused, superfluous ignore directives.

Invalid:

// Actually this line is valid since `export` means "used",
// so this directive is superfluous
// deno-lint-ignore no-unused-vars
export const foo = 42;

Valid:

export const foo = 42;