fetch-configlet_v3: Improve archive extraction logic

This gives a single source of truth for the name of the archive and for
the curl command.

It also gets around the fact that the `tar` command should probably have
had `-` previously to specify reading from `stdin`.

scripts/fetch-configlet_v3

@@ -45,12 +45,12 @@ get_download_url() {
 }
 
 download_url="$(get_download_url)"
+output_path="bin/latest-configlet.${ext}"
+curl "${curlopts[@]}" "${download_url}" -o "${output_path}"
 
 case "${ext}" in
-    *zip)
-        curl "${curlopts[@]}" "${download_url}" -o bin/latest-configlet.zip
-        unzip bin/latest-configlet.zip -d bin/
-        rm bin/latest-configlet.zip
-        ;;
-    *) curl "${curlopts[@]}" "${download_url}" | tar xz -C bin/ ;;
+    *zip) unzip "${output_path}" -d bin/   ;;
+    *)    tar xzf "${output_path}" -C bin/ ;;
 esac
+
+rm -f "${output_path}"