Makefile: simplify; clean removes images

The target all was previous running setup followed by build.  As
both setup and build are phony targets they run in sequence and because
the firmware contain the timestamp they always run (dependencies doesn't
do anything).  all now does exactly what it says on the tin
without introducing non-standard targets.

clean now removes the images that created during build which is
what you expect from that target.  See:
https://www.gnu.org/software/make/manual/html_node/Standard-Targets.html#Standard-Targets

Makefile

@@ -1,21 +1,16 @@
-TIMESTAMP := $(shell date -u +"%Y%m%d%H%M%S")
 DOCKER := $(shell { command -v podman || command -v docker; })
+TIMESTAMP := $(shell date -u +"%Y%m%d%H%M%S")
 
-.PHONY: clean setup
-
-all: setup build
-
-build: firmware/$$(TIMESTAMP)-left.uf2 firmware/$$(TIMESTAMP)-right.uf2
+.PHONY: all clean
 
-clean:
-	rm -f firmware/*.uf2
-
-firmware/%-left.uf2 firmware/%-right.uf2: config/adv360.keymap
+all:
+	$(DOCKER) build --tag zmk --file Dockerfile .
 	$(DOCKER) run --rm -it --name zmk \
 		-v $(PWD)/firmware:/app/firmware \
 		-v $(PWD)/config:/app/config:ro \
 		-e TIMESTAMP=$(TIMESTAMP) \
 		zmk
 
-setup: Dockerfile bin/build.sh config/west.yml
-	$(DOCKER) build --tag zmk --file Dockerfile .
+clean:
+	rm -f firmware/*.uf2
+	$(DOCKER) image rm zmk docker.io/zmkfirmware/zmk-build-arm:stable