Remove redundant GC.dispose() calls for Image objects

This minor refactoring eliminates unnecessary calls to GC.dispose() since disposing an Image automatically disposes its associated GC. There is no visual impact from this change.

Author: arunjose696

bundles/org.eclipse.jface/src/org/eclipse/jface/preference/ColorSelector.java

@@ -192,7 +192,6 @@ private ImageData getImageData(int zoom) {
 		}
 		gc.setLineWidth(2);
 		gc.drawRectangle(image.getBounds());
-		gc.dispose();
 
 		ImageData data = image.getImageData(zoom);
 		image.dispose();