There are two type of events:

* command events (`openSidebar`, `closeSidebar`): direct the receiving
  frame to take an specific action.

* information events ('sidebarOpened`, `helpRequested`): informs the
  receiving frame that an action _already_ took place, in case a follow
  up action needs to happen.

The `destroyFrame` aligns more with the second type.

Follow up of: https://github.com/hypothesis/client/pull/3838/files#r731077947