HID: hid-lg3ff: remove unused struct lg3ff_device

struct lg3ff_device is present in the driver since its addition by
commit 74f292ca (HID: add driver for the Logitech Flight System
G940).

But it was never used, remove it.

Found by https://github.com/jirislaby/clang-struct.
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Gary Stein <LordCnidarian@gmail.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

drivers/hid/hid-lg3ff.c

@@ -41,10 +41,6 @@
  * I'm sure these are effects that I don't know enough about them
  */
 
-struct lg3ff_device {
-	struct hid_report *report;
-};
-
 static int hid_lg3ff_play(struct input_dev *dev, void *data,
 			 struct ff_effect *effect)
 {