Remove tempest/manager.py after 4 year deprecation

tempest/manager.py has been deprecated for over 4 years already,
it's time to remove it.

Implements: blueprint tempest-scenario-manager-stable
Change-Id: Iea813d478a93a1638be597af48929cd50a5e6366
diff --git a/releasenotes/notes/Remove-manager-2e0b0af48f01294a.yaml b/releasenotes/notes/Remove-manager-2e0b0af48f01294a.yaml
new file mode 100644
index 0000000..822df7d
--- /dev/null
+++ b/releasenotes/notes/Remove-manager-2e0b0af48f01294a.yaml
@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    In this release tempest/manager.py is removed after more than 4 years
+    of deprecation.