Revert "Rename Do Not Disturb -> Priority Mode"

Revert submission 16632971-yl-prioritymode

Reason for revert: We're not launching this change with T, so this will revert all the relevant string changes.
Reverted Changes:
I5eff72db8:Rename Do Not Disturb -> Priority Mode
Ie7a9e35e6:Rename Do Not Disturb -> Priority Mode
I7bb74d2fd:Rename Do Not Disturb -> Priority Mode
Id17942024:Rename Do Not Disturb -> Priority Mode
Ib8efd7289:Rename Do Not Disturb -> Priority Mode
Ia1b77f9ee:Rename Do Not Disturb -> Priority Mode

Bug: 190180868
Test: TH

Change-Id: I7516c97809c7968f999d7caa8885f0cb5cdc844f
Merged-In: I7516c97809c7968f999d7caa8885f0cb5cdc844f