Move roaming icon to upper left.

- Update stat_sys_roaming to the new M2 icon
- Move the R icon to be displayed in the upper left corner of the signal
icon instead of centered to the right
- Also remove unncessary extra SignalDrawable in SignalClusterView

Fixes: 72540392
Test: visual
Change-Id: I4ac0e160b0f262bf6912f61f0817b778634be1ad