(maint) Stop building alpine image

The puppet-agent-alpine image is based on an unmaintained version of alpine and
would require significant work to update, since it builds all puppet-agent
components from source and compiles against musl.

This keeps the ubuntu image which is published as `puppet-agent-ubuntu` and
`puppet-agent`.

Makefile

@@ -5,7 +5,6 @@ build_date := $(shell date -u +%FT%T)
 hadolint_available := $(shell hadolint --help > /dev/null 2>&1; echo $$?)
 hadolint_command := hadolint
 hadolint_container := ghcr.io/hadolint/hadolint:latest
-alpine_version := 3.9
 ubuntu_version := 18.04
 export BUNDLE_PATH = $(PWD)/.bundle/gems
 export BUNDLE_BIN = $(PWD)/.bundle/bin
@@ -25,41 +24,32 @@ prep:
 lint:
 ifeq ($(hadolint_available),0)
 	@$(hadolint_command) puppet-agent-ubuntu/$(dockerfile)
-	@$(hadolint_command) puppet-agent-alpine/$(dockerfile)
 else
 	@docker pull $(hadolint_container)
 	@docker run --rm -v $(PWD)/puppet-agent-ubuntu/$(dockerfile):/Dockerfile -i $(hadolint_container) $(hadolint_command) Dockerfile
-	@docker run --rm -v $(PWD)/puppet-agent-alpine/$(dockerfile):/Dockerfile -i $(hadolint_container) $(hadolint_command) Dockerfile
 endif
 
 build: prep
-	docker pull alpine:$(alpine_version)
 	docker pull ubuntu:$(ubuntu_version)
 	docker build ${DOCKER_BUILD_FLAGS} --build-arg ubuntu_version=$(ubuntu_version) --build-arg vcs_ref=$(vcs_ref) --build-arg build_date=$(build_date) --build-arg version=$(version) --file puppet-agent-ubuntu/$(dockerfile) --tag $(NAMESPACE)/puppet-agent-ubuntu:$(version) puppet-agent-ubuntu
 	@docker tag $(NAMESPACE)/puppet-agent-ubuntu:$(version) $(NAMESPACE)/puppet-agent:$(version)
-	docker build ${DOCKER_BUILD_FLAGS} --build-arg alpine_version=$(alpine_version) --build-arg vcs_ref=$(vcs_ref) --build-arg build_date=$(build_date) --build-arg version=$(version) --file puppet-agent-alpine/$(dockerfile) --tag $(NAMESPACE)/puppet-agent-alpine:$(version) $(PWD)/..
 ifeq ($(IS_LATEST),true)
 	@docker tag $(NAMESPACE)/puppet-agent-ubuntu:$(version) $(NAMESPACE)/puppet-agent-ubuntu:$(LATEST_VERSION)
 	@docker tag $(NAMESPACE)/puppet-agent-ubuntu:$(version) $(NAMESPACE)/puppet-agent:$(LATEST_VERSION)
-	@docker tag $(NAMESPACE)/puppet-agent-alpine:$(version) $(NAMESPACE)/puppet-agent-alpine:$(LATEST_VERSION)
 endif
 
 test: prep
 	@bundle install --path $$BUNDLE_PATH --gemfile $$GEMFILE --with test
 	@bundle update
 	@PUPPET_TEST_DOCKER_IMAGE=$(NAMESPACE)/puppet-agent-ubuntu:$(version) \
 		bundle exec --gemfile $$GEMFILE rspec spec
-	@PUPPET_TEST_DOCKER_IMAGE=$(NAMESPACE)/puppet-agent-alpine:$(version) \
-		bundle exec --gemfile $$GEMFILE rspec spec
 
 publish: prep
 	@docker push $(NAMESPACE)/puppet-agent-ubuntu:$(version)
 	@docker push $(NAMESPACE)/puppet-agent:$(version)
-	@docker push $(NAMESPACE)/puppet-agent-alpine:$(version)
 ifeq ($(IS_LATEST),true)
 	@docker push $(NAMESPACE)/puppet-agent-ubuntu:$(LATEST_VERSION)
 	@docker push $(NAMESPACE)/puppet-agent:$(LATEST_VERSION)
-	@docker push $(NAMESPACE)/puppet-agent-alpine:$(LATEST_VERSION)
 endif
 
 .PHONY: lint build test publish