fix: staticcheck and deadcode findings repo-wide, modernize counting loops

cmd/gasm/audit.go

@@ -66,7 +66,7 @@ mnemonic, so the audit tracks whatever toolchain `+"`go env GOROOT`"+` names.
 		return err
 	}
 
-	var superset, backlog, shared, goOnly []string
+	var superset, backlog, shared []string
 	for _, name := range names {
 		switch {
 		case !asm.Encodable(name):
@@ -77,16 +77,8 @@ mnemonic, so the audit tracks whatever toolchain `+"`go env GOROOT`"+` names.
 			shared = append(shared, name)
 		}
 	}
-	for _, name := range names {
-		if goKnown[name] && !seen[name] {
-			goOnly = append(goOnly, name)
-		}
-	}
-	// GO-ONLY is computed from the complement of the gasm table, which this
-	// audit cannot enumerate (Go's table is only visible through probes of
-	// names we already know).  Report it as informational zero instead of a
-	// misleading list.
-	goOnly = nil
+	// GO-ONLY is not enumerable by probing: Go's table is only visible
+	// through names we already know, so nothing can be reported there.
 
 	sort.Strings(superset)
 	sort.Strings(backlog)