Remove DOCKER_HTTP_HOST_COMPAT env var

Signed-off-by: Darren Shepherd <darren@rancher.com>

cmd/dockerd/daemon_unix.go

@@ -114,7 +114,6 @@ func notifyShutdown(err error) {
 }
 
 func wrapListeners(proto string, ls []net.Listener) []net.Listener {
-	if os.Getenv("DOCKER_HTTP_HOST_COMPAT") != "" {
 	switch proto {
 	case "unix":
 		ls[0] = &hack.MalformedHostHeaderOverride{ls[0]}
@@ -123,6 +122,5 @@ func wrapListeners(proto string, ls []net.Listener) []net.Listener {
 			ls[i] = &hack.MalformedHostHeaderOverride{ls[i]}
 		}
 	}
-	}
 	return ls
 }

docs/reference/commandline/dockerd.md

@@ -849,20 +849,6 @@ set like this:
     export DOCKER_TMPDIR=/mnt/disk2/tmp
     /usr/local/bin/dockerd -D -g /var/lib/docker -H unix:// > /var/lib/docker-machine/docker.log 2>&1
 
-Docker clients <= 1.9.2 used an invalid Host header when making request to the
-daemon. Docker 1.12 is built using golang 1.6 which is now checking the validity
-of the Host header and as such clients <= 1.9.2 can't talk anymore to the daemon.
-Docker supports overcoming this issue via a Docker daemon
-environment variable. In case you are seeing this error when contacting the
-daemon:
-
-    Error response from daemon: 400 Bad Request: malformed Host header
-
-The `DOCKER_HTTP_HOST_COMPAT` can be set like this:
-
-    DOCKER_HTTP_HOST_COMPAT=1 /usr/local/bin/dockerd ...
-
-
 ## Default cgroup parent
 
 The `--cgroup-parent` option allows you to set the default cgroup parent