fix: remove Buildarch from globals, main, Makefile, logger, and tests

Buildarch was erroneously included. Remove it from:
- internal/globals/globals.go (struct field, package var, setter)
- cmd/dnswatcher/main.go (var declaration, setter call)
- Makefile (BUILDARCH var, ldflags)
- internal/logger/logger.go (Identify log field)
- internal/config/config_test.go (test fixture)
- README.md (build command, architecture section)

internal/config/config_test.go

@@ -19,9 +19,8 @@ func newTestParams(t *testing.T) config.Params {
 	t.Helper()
 
 	g := &globals.Globals{
-		Appname:   "dnswatcher",
-		Version:   "test",
-		Buildarch: "amd64",
+		Appname: "dnswatcher",
+		Version: "test",
 	}
 
 	l, err := logger.New(nil, logger.Params{Globals: g})