refactor: remove BgTabReplaced, doesn't exist in Firefox

src/Model/Events.purs

@@ -21,7 +21,6 @@ data BackgroundEvent
   | BgTabAttached Tab
   | BgTabDetached TabId
   | BgTabHighlighted
-  | BgTabReplaced
   | BgTabZoomChanged
 
 derive instance genBackgroundEvent :: Generic BackgroundEvent _

src/Sidebar/Sidebar.purs

@@ -70,7 +70,6 @@ onBackgroundMsgConsumer query =
           void $ query $ H.tell $ Tabs.TabAttached tab
           pure Nothing
         BgTabHighlighted -> pure Nothing
-        BgTabReplaced -> pure Nothing
         BgTabZoomChanged -> pure Nothing
 
 onSidebarMsg :: Runtime.Port -> CR.Consumer SidebarEvent Aff Unit