Simply detection of PROTOC archive file name

The introduction of a new ARCH variable was unnecessary, as ARCH already
exists. That said, the .zip provided for PROTOC isn't a natural fit
here either, as upsream uses `aarch_64` rather than `aarch64`.

In stead, I've used `notdir` to get the filename from the
already-defined `PROTOC_URL`.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

Variables.mk

@@ -83,8 +83,6 @@ CONFIG := $(shell pwd)
 # helper functions
 godeps=$(shell go list -deps -f '{{if not .Standard}}{{ $$dep := . }}{{range .GoFiles}}{{$$dep.Dir}}/{{.}} {{end}}{{end}}' $(1) | sed "s%${PWD}/%%g")
 
-ARCHITECTURE_CPU=$(shell lscpu | grep 'Architecture' | cut -d':' -f2 | xargs)
-
 # use GOPROXY for older git clients and speed up downloads
 GOPROXY ?= https://proxy.golang.org
 export GOPROXY