chore: cleanup Makefile

It's important to keep Makefile clean.

- Every goal should be a PHONY
- It is not necessary to check if the programs are available.
  - For example, users may want to upgrade to the new versions.

Author: kkweon

Makefile

@@ -1,29 +1,24 @@
-.PHONY: all
 .DEFAULT_GOAL := all
 
-PROTOC := $(shell which protoc)
-PROTOC_GEN_GO := $(shell which protoc-gen-go)
-PROTOC_VERSION := 3.17.0
+PROTOC_VERSION := 3.17.2
 PROTOC_RELEASE := https://github.com/protocolbuffers/protobuf/releases
 PROTO_FILES := $(shell find . -name "*.proto" -type f)
 UNAME := $(shell uname)
-GOPATH := ${GOPATH}
 
+.PHONY: install
 install:
-ifeq ($(PROTOC),)
 ifeq ($(UNAME),Darwin)
 	brew install protobuf
 endif
 ifeq ($(UNAME), Linux)
 	curl -LO "$(PROTOC_RELEASE)/download/v$(PROTOC_VERSION)/protoc-$(PROTOC_VERSION)-linux-x86_64.zip" && \
 	unzip protoc-$(PROTOC_VERSION)-linux-x86_64.zip -d $${HOME}/.local && \
 	export PATH="$${PATH}:$${HOME}/.local/bin"
+	rm protoc-*.zip
 endif
-endif
-ifeq ($(PROTOC_GEN_GO),)
 	go mod download && grep _ ./cmd/tools/tools.go | cut -d' ' -f2 | sed 's/\r//' | xargs go install -v
-endif
 
+.PHONY: all
 all:
 	mkdir -p ./pkg/pbs/
 	protoc \
@@ -34,5 +29,6 @@ all:
     --go-grpc_opt=paths=source_relative \
     $(PROTO_FILES)
 
+.PHONY: clean
 clean:
 	rm -rf ./pkg/pbs/*.pb.go