CT-1568 add CasesController#remove_clearance for clarity
CT-1568 add CasesController#remove_clearance for clarity

This action doesn't need to do anything, but it'd be nice if it was there, so
that it's less confusing when trying to understand the system, and if it
authorized to ensure that users don't even think they can remove clearance if
they happen to get to load this page somehow.

ministryofjustice/correspondence_tool_staff,ministryofjustice/correspondence_tool_staff,ministryofjustice/correspondence_tool_staff,ministryofjustice/correspondence_tool_staff,ministryofjustice/correspondence_tool_staff