usb: dwc3: debugfs: delete redandunt dwc3_debugfs_create_endpoint_dirs

Since mainline commit 8d396bb0 ("usb: dwc3: debugfs: Add and remove
endpoint dirs dynamically") drops dwc3_debugfs_create_endpoint_dirs(),
let's delete it in dwc3_debugfs_init either.

Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>