Recompress old change screen screenshot with pngcrush

This reduces the size of the file by approx 35% and makes
it viewable on my Macbook Pro.

Change-Id: Ie8956ee336441ca2d9a9bff9b99d89314434da5f
diff --git a/img/old-change-screen.png b/img/old-change-screen.png
index dc31542..3dd6885 100644
--- a/img/old-change-screen.png
+++ b/img/old-change-screen.png
Binary files differ