HALO cleanup

hdpi and mdpi drawables were inconsistent, if you plan to use HALO on
lower res devices you must reproduce them.

Change-Id: I2746837bacd60c3079ace4c7523a68b8cd415f5f
HALO: new drawables for hdpi and mdpi

- scaled down the xhdpi drawables properly for hdpi and mdpi
- removed some old and unused halo pngs