gui(controls) remove redundant DOMImage declarations

gui/src/controls/checkbox.ts

@@ -1,7 +1,5 @@
 /// <reference path="../../../dist/preview release/babylon.d.ts"/>
 
-var DOMImage = Image;
-
 module BABYLON.GUI {
     export class Checkbox extends Control {
         private _isChecked = false;

gui/src/controls/colorpicker.ts

@@ -1,7 +1,5 @@
 /// <reference path="../../../dist/preview release/babylon.d.ts"/>
 
-var DOMImage = Image;
-
 module BABYLON.GUI {
     export class ColorPicker extends Control {
         private _colorWheelCanvas: HTMLCanvasElement;

gui/src/controls/line.ts

@@ -1,7 +1,5 @@
 /// <reference path="../../../dist/preview release/babylon.d.ts"/>
 
-var DOMImage = Image;
-
 module BABYLON.GUI {
     export class Line extends Control {
         private _lineWidth = 1;

gui/src/controls/radioButton.ts

@@ -1,7 +1,5 @@
 /// <reference path="../../../dist/preview release/babylon.d.ts"/>
 
-var DOMImage = Image;
-
 module BABYLON.GUI {
     export class RadioButton extends Control {
         private _isChecked = false;

gui/src/controls/slider.ts

@@ -1,7 +1,5 @@
 /// <reference path="../../../dist/preview release/babylon.d.ts"/>
 
-var DOMImage = Image;
-
 module BABYLON.GUI {
     export class Slider extends Control {
         private _thumbWidth = new ValueAndUnit(30, ValueAndUnit.UNITMODE_PIXEL, false);