Revert "Run stop b2g and start b2g with 'adb root' privs"

This reverts commit cedf51858c403f3b8c9db9ce76758a51617c8cd1.

I never really liked this patch and it turns out it doesn't work properly anymore with the latest Leo build.

We can (and do) create the same effect in the Jenkins by running adb in root mode before the test run.

`master` -> Merge
`v1-train` -> Merge