build: remove --enable-colo/--disable-colo

No need to provide this knob, so remove it and stubs/migration-colo.c.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -228,7 +228,6 @@ vhost_net="no"
 vhost_scsi="no"
 vhost_vsock="no"
 kvm="no"
-colo="yes"
 rdma=""
 gprof="no"
 debug_tcg="no"
@@ -920,10 +919,6 @@ for opt do
   ;;
   --enable-kvm) kvm="yes"
   ;;
-  --disable-colo) colo="no"
-  ;;
-  --enable-colo) colo="yes"
-  ;;
   --disable-tcg-interpreter) tcg_interpreter="no"
   ;;
   --enable-tcg-interpreter) tcg_interpreter="yes"
@@ -1372,7 +1367,6 @@ disabled with --disable-FEATURE, default is enabled if available:
   fdt             fdt device tree
   bluez           bluez stack connectivity
   kvm             KVM acceleration support
-  colo            COarse-grain LOck-stepping VM for Non-stop Service
   rdma            RDMA-based migration support
   vde             support for vde network
   netmap          support for netmap network
@@ -5062,7 +5056,6 @@ echo "Linux AIO support $linux_aio"
 echo "ATTR/XATTR support $attr"
 echo "Install blobs     $blobs"
 echo "KVM support       $kvm"
-echo "COLO support      $colo"
 echo "RDMA support      $rdma"
 echo "TCG interpreter   $tcg_interpreter"
 echo "fdt support       $fdt"
@@ -5701,10 +5694,6 @@ if have_backend "syslog"; then
 fi
 echo "CONFIG_TRACE_FILE=$trace_file" >> $config_host_mak
 
-if test "$colo" = "yes"; then
-  echo "CONFIG_COLO=y" >> $config_host_mak
-fi
-
 if test "$rdma" = "yes" ; then
   echo "CONFIG_RDMA=y" >> $config_host_mak
 fi