DialpadView cleanup.

Changes:
1. Rewrote the logic to pick a NumberFormat.
2. Deleted dead method setShowVoicemailButton(boolean) and field mCanDigitsBeEdited.
3. Deleted the redundant SDK version check when getting a Drawable.
Test: DialpadFragmentIntegrationTest
PiperOrigin-RevId: 176181808
Change-Id: Iee4e3db8535ebbea3d4c63c8d8c1d3eb342b538e