usb: remove old usb-host code

The usb-host code has been rewritten for qemu 1.5 to use libusb,
the old code has been left in as temporary fallback.  Now we are
two releases further out, targeting the 1.7 release.  No major
issues with the new code poped up until now.  Time to remove it
from tre tree.  Should we ever need it again for some reason --
git has a copy for us in the history.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

configure

@@ -562,7 +562,6 @@ Haiku)
   audio_possible_drivers="oss alsa sdl esd pa"
   linux="yes"
   linux_user="yes"
-  usb="linux"
   kvm="yes"
   vhost_net="yes"
   vhost_scsi="yes"
@@ -575,9 +574,6 @@ esac
 
 if [ "$bsd" = "yes" ] ; then
   if [ "$darwin" != "yes" ] ; then
-    if [ "$targetos" != "FreeBSD" ]; then
-      usb="bsd"
-    fi
     bsd_user="yes"
   fi
 fi
@@ -3126,7 +3122,6 @@ fi
 if test "$libusb" != "no" ; then
     if $pkg_config --atleast-version=1.0.13 libusb-1.0; then
         libusb="yes"
-	usb="libusb"
         libusb_cflags=$($pkg_config --cflags libusb-1.0)
         libusb_libs=$($pkg_config --libs libusb-1.0)
         QEMU_CFLAGS="$QEMU_CFLAGS $libusb_cflags"
@@ -4166,24 +4161,11 @@ if test "$virtio_blk_data_plane" = "yes" ; then
 fi
 
 # USB host support
-case "$usb" in
-linux)
-  echo "HOST_USB=linux legacy" >> $config_host_mak
-;;
-bsd)
-  echo "HOST_USB=bsd" >> $config_host_mak
-;;
-libusb)
-  if test "$linux" = "yes"; then
-    echo "HOST_USB=libusb linux legacy" >> $config_host_mak
-  else
-    echo "HOST_USB=libusb legacy" >> $config_host_mak
-  fi
-;;
-*)
+if test "$libusb" = "yes"; then
+  echo "HOST_USB=libusb legacy" >> $config_host_mak
+else
   echo "HOST_USB=stub" >> $config_host_mak
-;;
-esac
+fi
 
 # TPM passthrough support?
 if test "$tpm" = "yes"; then