global: get rid of nonnull gradle hack

Hacking things up via gradle is not right, and package-info.java poses
problems with two modules, so instead we just apply it manually to every
class.

Remember to add this to new classes!

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tunnel/src/main/java/com/wireguard/android/util/RootShell.java

@@ -5,6 +5,8 @@
 
 package com.wireguard.android.util;
 
+import com.wireguard.util.NonNullForAll;
+
 import android.content.Context;
 import androidx.annotation.Nullable;
 import android.util.Log;
@@ -24,6 +26,7 @@ import java.util.UUID;
  * Helper class for running commands as root.
  */
 
+@NonNullForAll
 public class RootShell {
     private static final String SU = "su";
     private static final String TAG = "WireGuard/" + RootShell.class.getSimpleName();