Replace bluetooth pngs with vector drawables.

The current pngs are hardcoded to the green accent color.
Instead, the new vector drawable replacements have colorAccent
set as a tint.

Saves a bit on APK size, especially since ic_bt_cellphone
can be auto-mirrored rather than requiring ldrtl variants.

BUG: 28760785
Change-Id: Ifaec204ad28dd6cbd8463388080583bf7cf62044