usb: gadget: fusb300_udc: drop dead code

that code has been dead forever. Since the
first commit (0fe6f1d1) the use of that code
has been commented out. Let's drop the dead
code already and fix the following compile
warning:

| drivers/usb/gadget/fusb300_udc.c: At top level:
| drivers/usb/gadget/fusb300_udc.c:771:13: warning: ‘fusb300_wrfifo’ defined but not used [-Wunused-function]
| drivers/usb/gadget/fusb300_udc.c:1027:13: warning: ‘fusb300_set_ep_bycnt’ defined but not used [-Wunused-function]

Signed-off-by: Felipe Balbi <balbi@ti.com>