Set scrollbars to none on EnableZenModeDialog description text.

This is the text that says "Until 5:07PM" (for example) to demonstrate how long one would be turning DND on. For some reason, it was showing a scrollbar on the dialog that opens from Settings (but not Quick Settings).

Bug: 349845540
Test: manual
Flag: EXEMPT unflaggable
Change-Id: I57cbd00a96818b1f7bc1a36660200fac1839335c