Fix over-sized images in drawable-sw600dp.

We have both drawable-sw600dp/ and drawable-sw600dp-mdpi/. We are getting
images from drawable-sw600dp/ and they are too large. Those over-sized images
are removed, and to avoid confusion, move the images in drawable-sw600dp-mdpi/
to drawable-sw600dp/.

Bug: 6549010
Change-Id: Ibd6dea8aec3740c4e6d5992ccdba3518fbb89a23