DynamicSystem string review followup

Some changes to follow string review suggestions:
- Simplify some messages.
- Replace 'Reboot' with 'Restart'.
- Notification action button order: 'Restart' button on the right.

Bug: 129100345
Test: verified with test app
Change-Id: I1ee97b0adbf74add68d3561fc647dc4923ee7237