Only show app icon + limit 2 lines toast on targetSdk S+

- Apps that don't yet target S will not show their app icon nor be limited
to 2 line toasts.
- Remove toast flag. Always show new toast ui and animation.
- Update ToastUITest to check new UI behavior

Test: manually install app targetting sdk < S, check 2+ lines + no app
icon
Test: manually install app targetting sdk S, check max 2 lines + see app
icon
Test: atest ToastUITest
Bug: 188914179

Change-Id: I2f4251ae2eabde5bd43f22e14d8edca200562e65