Remove unused code

platform/firefox/vapi-background.js

@@ -1556,19 +1556,6 @@ vAPI.contextMenu.create = function(details, callback) {
 
 /******************************************************************************/
 
-vAPI.contextMenu.remove = function() {
-    for ( var win of vAPI.tabs.getWindows() ) {
-        this.unregister(win.document);
-    }
-
-    this.menuItemId = null;
-    this.menuLabel = null;
-    this.contexts = null;
-    this.onCommand = null;
-};
-
-/******************************************************************************/
-
 vAPI.lastError = function() {
     return null;
 };