What is the simplest change that I can make to a new Blank Activity, as created by the latest version of Android Studio, to get the app to appear fullscreen?
I want
You are getting this problem because the activity you are trying to apply the android:theme="@android:style/Theme.Holo.Light.NoActionBar.Fullscreen"> to is extending ActionBarActivity which requires the AppCompat theme to be applied.
Extend your activity from Activity rather than from ActionBarActivity
You might have to change your Java class accordingly little bit.
If you want to remove status bar too then use this before setContentView(layout) in onCreateView method
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);