stop changing scripts so that they work only on linux , please

we shouldn't never specify a specific screen implementation in the
examples, otherwise they won't run on platforms where that
implementation is not available.

We should always try asking for the default implemenation for the
platform we are running on (by omitting the argument when requesting for
the screen pointer)

scripts/javascript/examples/test_rand.js

@@ -8,7 +8,7 @@
 W = 400;
 H = 300;
 
-scr = new Screen("sdl");
+scr = new Screen();
 scr.init(W,H);
 add_screen(scr);