[polari] mainWindow: Remove excess argument

[Florian Müllner <fmuellner src gnome org>]

commit 1f6db9cd56d4178432f2ca56f5dad5ffa3193e9a
Author: Florian Müllner <fmuellner gnome org>
Date:   Sun Apr 9 21:25:55 2017 +0200

    mainWindow: Remove excess argument
    
    Meh, this line has been touched a couple of times since commit
    4314b205b, but this (sic) always made it through somehow ...

 src/mainWindow.js |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/mainWindow.js b/src/mainWindow.js
index 229c3fb..a6c6b4b 100644
--- a/src/mainWindow.js
+++ b/src/mainWindow.js
@@ -234,7 +234,7 @@ const MainWindow = new Lang.Class({
 
     _onSizeAllocate: function(widget, allocation) {
         if (!this._isFullscreen && !this._isMaximized)
-            this._currentSize = this.get_size(this);
+            this._currentSize = this.get_size();
     },
 
     _onDestroy: function(widget) {