fix: clean up after cp'ing script [ci skip]

Follows 31e0ed75b0.

Makefile

@@ -32,9 +32,8 @@ build-kadabra:
 build: build-abra build-kadabra
 
 build-docker-abra:
-	@docker run -it \
+	@docker run -it -v $(PWD):/abra golang:$(GOVERSION) \
-		-v $(PWD):/abra golang:$(GOVERSION) \
+		bash -c 'cd /abra; cp scripts/docker/build.sh .; ./build.sh; rm build.sh'
-		bash -c 'cd /abra; mv scripts/docker/build.sh .; ./build.sh'
 
 build-docker: build-docker-abra