Handle raw Google KMS signatures

Scripts/release/google-kms-openssl-dgst-shim.sh

@@ -187,11 +187,10 @@ trap 'rm -f "$encoded_signature_file"' EXIT
   --quiet >/dev/null
 
 python3 - "$encoded_signature_file" "$signature_file" <<'PY'
-import base64
 import pathlib
 import sys
 
 encoded_path = pathlib.Path(sys.argv[1])
 signature_path = pathlib.Path(sys.argv[2])
-signature_path.write_bytes(base64.b64decode(encoded_path.read_text(encoding="utf-8").strip()))
+signature_path.write_bytes(encoded_path.read_bytes())
 PY