spectators: Use display: inherit for only-visible-to-spectators.

The previous `display: unset` logic didn't work with dividers in the
gear menu. This new version should be correct -- what we want to do
here is just override the `display: none` default for this class, not
revert to the default browser styling for that element type.

static/styles/app_components.css

@@ -605,7 +605,7 @@ div.overlay {
     }
 
     .only-visible-for-spectators {
-        display: unset;
+        display: inherit;
     }
 }