Update instant app notification icon.

- No more circle. That is only meant for badges.
- http://go/aia-branding for more details.

Screenshots:
https://screenshot.googleplex.com/zmN3oFSLNkj (before)
https://screenshot.googleplex.com/wdtT9qN0h5q (after)

Test: Screenshot above from marlin.
Bug: 65430504
Change-Id: I53c362b29b2f0401d5abd9a3ad439add23f80f5b