Makefile: remove unused BUILD_APT_MIRROR

BUILD_APT_MIRROR added in https://github.com/moby/moby/pull/26375
is not used anymore.

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

Makefile

@@ -27,7 +27,6 @@ export VALIDATE_ORIGIN_BRANCH
 # make DOCKER_LDFLAGS="-X github.com/docker/docker/daemon/graphdriver.priority=overlay2,zfs" dynbinary
 #
 DOCKER_ENVS := \
-	-e BUILD_APT_MIRROR \
 	-e BUILDFLAGS \
 	-e KEEPBUNDLE \
 	-e DOCKER_BUILD_ARGS \
@@ -107,8 +106,6 @@ DOCKER_PORT_FORWARD := $(if $(DOCKER_PORT),-p "$(DOCKER_PORT)",)
 DELVE_PORT_FORWARD := $(if $(DELVE_PORT),-p "$(DELVE_PORT)",)
 
 DOCKER_FLAGS := $(DOCKER) run --rm --privileged $(DOCKER_CONTAINER_NAME) $(DOCKER_ENVS) $(DOCKER_MOUNT) $(DOCKER_PORT_FORWARD) $(DELVE_PORT_FORWARD)
-BUILD_APT_MIRROR := $(if $(DOCKER_BUILD_APT_MIRROR),--build-arg APT_MIRROR=$(DOCKER_BUILD_APT_MIRROR))
-export BUILD_APT_MIRROR
 
 SWAGGER_DOCS_PORT ?= 9000
 
@@ -144,7 +141,7 @@ ifdef DOCKER_SYSTEMD
 DOCKER_BUILD_ARGS += --build-arg=SYSTEMD=true
 endif
 
-BUILD_OPTS := ${BUILD_APT_MIRROR} ${DOCKER_BUILD_ARGS} ${DOCKER_BUILD_OPTS}
+BUILD_OPTS := ${DOCKER_BUILD_ARGS} ${DOCKER_BUILD_OPTS}
 BUILD_CMD := $(BUILDX) build
 BAKE_CMD := $(BUILDX) bake