usb: gadget: fusb300: remove #if 0 block

The code in this block is unused and the Author is fine with removing:

| These functions were used to debug unstable hw fifo while developing
| fusb300.  It's much more stable now.
| So these functions can be removed.

Cc: "Wendy Yuan-Hsin Chen" <yhchen@faraday-tech.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>