Change getService (deprecated) to waitForService

The `getService` method is now deprecated. This changes the
getService calls to waitForService.

The only potential difference in functionality is that getService
times out after 10 seconds, while waitForService waits indefinitely.

Test: flash to device and reboot,
  `adb logcat | egrep -i "twoshay|flinger"`
  shows nothing suspiciously different before/after the change.

Bug: 265069414
Change-Id: I84c5f860c869a4e11be6e5490268920dae1e29cc