examples: hello_world: Drop inclusion of common header

The "common.h" header is not covered by the licensing exception for
standalone applications. Let's drop inclusion of this header from the
hello_world example to prove that a standalone app can be built without
it.

Signed-off-by: Paul Barker <paul.barker@sancloud.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

examples/standalone/hello_world.c

@@ -4,7 +4,6 @@
  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
  */
 
-#include <common.h>
 #include <exports.h>
 
 int hello_world(int argc, char *const argv[])