usb storage: remove inherited SCSI dependency for USB_STORAGE_ENE_UB6250

Because USB_STORAGE build symbol strictly depends on SCSI build
symbol, there is no need to specify it again.

In addition USB_STORAGE_ENE_UB6250 entry description repeats a note
about SCSI dependency from the parent USB_STORAGE entry description,
hence the change removes this duplication.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>