Fix corner roundness for pinned notifications

Sometimes the PINNED SourceType is not reset on transition from
floating HUN to shade. This causes heads up notifications to have
incorrectly rounded bottom corners despite having notifications
appear below them in the same section.

The PINNED SourceType is redundant because the HEADSUP
SourceType handles rounding for the same notifications.

For each HUN,
ExpandableNotificationRow request roundness for HEADSUP
HeadsUpAppearanceController requests roundness for PINNED

We can fix this bug by removing the redundant PINNED SourceType.
Fixes: 301261545

Test: send a lot of delayed HUNs, open shade
      => corners consistently correct

      swipe down on lockscreen/pulsing HUNs to open shade
      send delayed HUN while in fullscreen qs, close qs
      send HUN while scrolled, then unscroll
      horizontal swipe to dismiss single notifs
      clear all notifs
      => no corner regressions

Change-Id: Iadc76c251a77582f1c99652172fda882ce7d8abf