CI: Drop test-artifacts/Makefile

This is unused since commit 3c0c177ff9 ("CI: Switch qemu-arm* jobs to using
the distro provided QEMU"), and wants never to return.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Denis Mukhin <dmukhin@ford.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

automation/tests-artifacts/Makefile

@@ -1,19 +0,0 @@
-
-# the base of where these containers will appear
-REGISTRY := registry.gitlab.com/xen-project/xen/tests-artifacts
-CONTAINERS = $(subst .dockerfile,,$(wildcard */*.dockerfile))
-
-help:
-	@echo "Containers to build and export tests artifacts."
-	@echo "To build one run 'make ARTIFACT/VERSION'. Available containers:"
-	@$(foreach file,$(sort $(CONTAINERS)),echo ${file};)
-	@echo "To push container builds, set the env var PUSH"
-
-%: %.dockerfile ## Builds containers
-	$(DOCKER_CMD) build --pull -t $(REGISTRY)/$(@D):$(@F) -f $< $(<D)
-	@if [ ! -z $${PUSH+x} ]; then \
-		$(DOCKER_CMD) push $(REGISTRY)/$(@D):$(@F); \
-	fi
-
-.PHONY: all
-all: $(CONTAINERS)