Don't generate a .php wrapper file by default

It's now only generated if something to put in it is specified via:

%pragma(php) include=...

or

%pragma(php) code=...

Examples/test-suite/php/pointer_reference_runme.php

@@ -1,7 +1,6 @@
 <?php
 
 require "tests.php";
-require "pointer_reference.php";
 
 $s  = pointer_reference::get();
 check::equal($s->value, 10, "pointer_reference::get() failed");