usb: dwc3: debugfs: remove test mode interface

usb: dwc3: debugfs: remove test mode interface

There are some issues around for enabling/disabling this mode and
handling it. It does not work perfectly (yet). However we have a few
gadgets tested successfuly so far. That means we are quite confident
that we won't need this in near future.
So I'm for removing it and bringing a working version back once there is
a need for it.

Thanks to Dan Carpenter who spotted the wrong memory handling here.

[ balbi@ti.com : made it actually apply ]

Cc: Dan Carpenter <error27@gmail.com>
Cc: wharms@bfs.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>