tempest-cleanup can only be invoked as tempest cleanup

The CLI entry point removed here points to the main() class which was removed
so that tempest-cleanup is not a standalone command anymore.

See I2119acd402b0985d4a81c85501ce7265f782d37b

Change-Id: I3421667916bf3652ab0e777fa78c382a3f6e849d
diff --git a/releasenotes/notes/tempest-cleanup-nostandalone-39df2aafb2545d35.yaml b/releasenotes/notes/tempest-cleanup-nostandalone-39df2aafb2545d35.yaml
new file mode 100644
index 0000000..20f310d
--- /dev/null
+++ b/releasenotes/notes/tempest-cleanup-nostandalone-39df2aafb2545d35.yaml
@@ -0,0 +1,5 @@
+---
+upgrade:
+  - the already depreacted tempest-cleanup standalone command has been
+    removed. The corresponding functionalities can be accessed through
+    the unified `tempest` command (`tempest cleanup`).