build(docker): remove explicit context

Makefile

@@ -2,7 +2,6 @@ REGISTRY	?= git.sakamoto.best/lolz
 IMAGE_NAME	?= auto-stars
 TAG			?= $(shell git rev-parse --short HEAD)
 IMAGE		:= $(REGISTRY)/$(IMAGE_NAME)
-CONTEXT		?= source
 DOCKERFILE	?= Dockerfile
 
 .PHONY: all build push clean
@@ -10,7 +9,7 @@ DOCKERFILE	?= Dockerfile
 all: push
 
 build:
-	docker build -f $(DOCKERFILE) -t $(IMAGE):$(TAG) -t $(IMAGE):latest $(CONTEXT)
+	docker build -f $(DOCKERFILE) -t $(IMAGE):$(TAG) -t $(IMAGE):latest
 
 push: build
 	docker push $(IMAGE):$(TAG)