code: private void removeMount(SlotReference slot) {
          mediaDetails.remove(slot);
          if (mediaMounts.remove(slot)) {
              deliverMountUpdate(slot, false);
          }
      }
docs: Records that there is no media mounted in a particular media player slot, updating listeners if this is a change,
  and clearing any affected items from our in-memory caches.
  
  @param slot the slot in which no media is mounted