remove test infrastructure dependency on running as admin

[stevenbrix]

This stemmed from #816, but we determined the task to remove the dependency on running as admin will take too much time, so it's getting a dedicated task.

Most of the functionality that requires running as admin can probably just be removed, such as JIT debugger registration. I personally don't see much value in that functionality, i can use gflags to do that if i want. There is a lot of ETW logging as well, and we'll need to handle that gracefully so that we can maintain this, although I doubt anyone will use it.