Revert "Use airflow_version in subject (#62)" (#64)

This reverts commit 38dfb510997635d7178c7e45a9c883d370397cfa.

dev/README_RELEASE_CLIENT.md

diff --git a/dev/README_RELEASE_CLIENT.md b/dev/README_RELEASE_CLIENT.md
index 43ea1aa..902b966 100644
--- a/dev/README_RELEASE_CLIENT.md
+++ b/dev/README_RELEASE_CLIENT.md
@@ -213,7 +213,7 @@
 
 ```shell script
 cat <<EOF
-[VOTE] Release Airflow Python Client ${VERSION_WITHOUT_RC} from Airflow ${AIRFLOW_VERSION}
+[VOTE] Release Airflow Python Client ${VERSION_WITHOUT_RC} from ${VERSION}
 EOF
 ```