de-dup images to fix incorrect texture scaling

when there are duplicate identical images in mdpi and hdpi directories
then the loaded textures are displayed skewed and repeated with black
line artifacts between them.

(cherry picked from commit 1a083eface547da1b0a6f7bcf4eead27e7582472)

Change-Id: I002f8c85829abd2a3c2862f981f9723f1daf59b9