cleanup: Remove empty init() functions

The method is optional, so there's no point at all in letting the
shell call an empty method during initialization.

https://gitlab.gnome.org/GNOME/gnome-shell-extensions/merge_requests/49

extensions/launch-new-instance/extension.js

@@ -2,9 +2,6 @@ const AppDisplay = imports.ui.appDisplay;
 
 let _activateOriginal = null;
 
-function init() {
-}
-
 function enable() {
   _activateOriginal = AppDisplay.AppIcon.prototype.activate;
   AppDisplay.AppIcon.prototype.activate = function() {

extensions/native-window-placement/extension.js

@@ -284,7 +284,3 @@ function disable() {
     global.stage.queue_relayout();
     resetState();
 }
-
-function init() {
-    /* do nothing */
-}

extensions/screenshot-window-sizer/extension.js

@@ -136,9 +136,6 @@ function cycleScreenshotSizes(display, window, binding) {
     flashMessage(message);
 }
 
-function init() {
-}
-
 function enable() {
     Main.wm.addKeybinding('cycle-screenshot-sizes',
                           Convenience.getSettings(),

extensions/windowsNavigator/extension.js

@@ -284,7 +284,3 @@ function disable() {
 
     resetState();
 }
-
-function init() {
-    /* do nothing */
-}