cleanup Trampoline

remove unused boolean and make private where possible

Bug: 118605476

Test: 1) atest RunFrameworksServicesRoboTests
2) atest TrampolineTest
3) flashed device and ran:adb shell bmgr backupnow --all
Ended with "Backup finished with result: Success". in logcat, there were
a few Scotty exceptions but those are known and ignorable as they come
from the server

Change-Id: I08fbe494f9268e80e8f16a8f66405ee8a743e9c3