Remove SKIPPED and HIDE constants #24
Description
Remove SKIPPED because:
It's only used in ChecklistController and that usage can be replaced with a workaround. Doesn't make sense to have a constant for this.
Remove HIDE because:
A check could provide information even if it's hidden (e.g. the logs would still show that it succeeded or a dependency was not met; or a Site Audit integration would be able to access these hidden check results), so hiding should be "closer to the front-end". A workaround would be storing a boolean with every check result that indicates whether it's hidden.