hmp-commands: Remove the deprecated usb_add and usb_del

hmp-commands: Remove the deprecated usb_add and usb_del

It's easy to use device_add and device_del as replacement instead.
The usb_add and usb_del commands are deprecated since QEMU 2.10,
and nobody complained that they are still needed, so let's get rid
of them now to make the HMP interface a little bit less overloaded.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1512073140-17672-1-git-send-email-thuth@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>