Remove `RootTargetPreparer` from odsign_e2e_tests.

Instead, we enable ADB root for individual test cases, and skip the test
case if ADB root is not supported. This allows us to run some test cases
that don't require root access on devices that don't support ADB root.

Bug: 214016309
Test: Run `odsign_e2e_tests` on a userdebug build and see all test cases
  pass.
Test: Run `odsign_e2e_tests` on a user build and see 2 test cases pass,
  while others are skipped.
Change-Id: I3d74800f5ce25555fec52ef65cbe57fcfe711907
4 files changed