usb: core: remove the Kconfig entry for USB_DEBUG

Since we have already removed the usage of CONFIG_USB_DEBUG, it is
meaningless that there is still a configuration entry for CONFIG_USB_DEBUG.
Signed-off-by: NPeter Chen <peter.chen@freescale.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/Kconfig

 #
 # USB Core configuration
 #
-config USB_DEBUG
-	bool "USB verbose debug messages"
-	help
-	  Say Y here if you want the USB core & hub drivers to produce a bunch
-	  of debug messages to the system log. Select this if you are having a
-	  problem with USB support and want to see more of what is going on.
-
 config USB_ANNOUNCE_NEW_DEVICES
 	bool "USB announce new devices"
 	help