Makefile: update protobuf generation instructions

The new instructions work with the latest protoc compiler, which
we can't use inside a Docker container anymore because the Docker
container is three years old and hasn't been updated since. The good
news is the compilation options have gotten much simpler, we don't
need to move files into place anymore.

Makefile

@@ -8,10 +8,7 @@ endif
 nothing:
 
 generate_proto:
-	docker run --rm -v $(PWD):$(PWD) -w $(PWD) znly/protoc -I. --go_out=Mgoogle/protobuf/field_mask.proto=github.com/google/go-genproto/protobuf/field_mask,plugins=grpc:./ ./google_libphonenumber/resources/*.proto
-	mv ./google_libphonenumber/resources/*.pb.go ./
-	sudo chown -R $(WHOAMI) *
-	$(SED_I) -E 's/package i18n_phonenumbers/package libphonenumber/g' $(shell ls *.pb.go)
+	protoc -I. --go_out=. --go_opt=Mgoogle_libphonenumber/resources/phonemetadata.proto=../libphonenumber --go_opt=Mgoogle_libphonenumber/resources/phonenumber.proto=../libphonenumber ./google_libphonenumber/resources/*.proto
 	awk '/static const unsigned char/ { show=1 } show; /}/ { show=0 }' ./google_libphonenumber/cpp/src/phonenumbers/metadata.cc | tail -n +2 | sed '$$d' | sed -E 's/([^,])$$/\1,/g' | awk 'BEGIN{print "package libphonenumber\nvar metaData = []byte{"}; {print}; END{print "}"}' > metagen.go
 	go fmt ./metagen.go