Remove obsolete proguard rules

mobile/proguard-rules.pro

@@ -20,10 +20,3 @@
 # If you keep the line number information, uncomment this to
 # hide the original source file name.
 #-renamesourcefileattribute SourceFile
-
--if public class be.mygod.librootkotlinx.RootServer {
-    private void doInit(android.content.Context, boolean, java.lang.String);
-}
--keep class be.mygod.librootkotlinx.RootServer {
-    public static void main(java.lang.String[]);
-}