Remove Buildarch from ldflags, use runtime.GOARCH instead

The architecture is available at runtime via stdlib, no need to bake
it in at build time.

Makefile

@@ -1,8 +1,7 @@
 .PHONY: check lint test fmt build clean
 
 VERSION := $(shell git describe --tags --always --dirty 2>/dev/null || echo "dev")
-BUILDARCH := $(shell go env GOARCH)
-LDFLAGS := -X main.Version=$(VERSION) -X main.Buildarch=$(BUILDARCH)
+LDFLAGS := -X main.Version=$(VERSION)
 
 # Default target: run all checks
 check: fmt-check lint test