usb: gadget: nokia: remove unused include

f_serial.c isn't necessary in nokia.c, we can
safely remove it.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/nokia.c

@@ -39,7 +39,6 @@
  */
 #include "f_ecm.c"
 #include "f_obex.c"
-#include "f_serial.c"
 #include "f_phonet.c"
 #include "u_ether.c"