Mms: Remove white background on the timestamp

The current white background clashes with the gradient
used for the background. It also causes a very slight
overdraw which theoretically hurts performance a bit.

Change-Id: Ib51df2abdb5f3f262d2983dc07635c03d0c75430
Fix a crash when scrolling while a SMS is delayed.

Change-Id: I73f2d5f0e44dd80955db58e29ce1712cbf4e0ebb