staging: dgap: remove redundant declarations.

These are already defined in dgap.h.
Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/dgap/dgap.c

@@ -158,12 +158,6 @@ static void dgap_err(char *s);
 /*
  * Function prototypes from dgap_sysfs.h
  */
-struct board_t;
-struct channel_t;
-struct un_t;
-struct pci_driver;
-struct class_device;
-
 static void dgap_create_ports_sysfiles(struct board_t *bd);
 static void dgap_remove_ports_sysfiles(struct board_t *bd);