deb: remove unused DOCKER_GOPATH variable

This variable was added in 09b3ac8
but appears to be unused.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit c4c6180)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Upstream-commit: e6539d2af3218e66767ef8175e02ba2e8e25ac42
Component: packaging

Author: thaJeztah

components/packaging/deb/common/rules

@@ -1,7 +1,6 @@
 #!/usr/bin/make -f
 
 VERSION ?= $(shell cat engine/VERSION)
-DOCKER_GOPATH := /go/src/github.com/docker
 
 override_dh_gencontrol:
 	# if we're on Ubuntu, we need to Recommends: apparmor