Updated LetterTileDrawable colors.

Now that LetterTileDrawable colors are the same as the colors used by
MaterialColorMapUtils, I unified the colors inside colors.xml and was
able to delete some MaterialColorMapUtils code.

BUG: 15889179
BUG: 16159407
Change-Id: I02b96011a30def913fb1de589aeb7a8c336e2154
3 files changed