Remove support of Debian 9

Debian 9 support was removed when we bumped the supported version to
10 during victoria cycle. Because we are transitioning stable/ussuri
to EOL, we no longer have to support that old version.

Change-Id: Ie535f1eba454ed804d7e8195eed5dfe64743cf01

metadata.json

@@ -17,7 +17,6 @@
         {
             "operatingsystem": "Debian",
             "operatingsystemrelease": [
-                "9",
                 "10",
                 "11"
             ]
@@ -40,7 +39,6 @@
             "operatingsystem": "Ubuntu",
             "operatingsystemrelease": [
                 "18.04",
-                "22.04",
                 "20.04",
                 "22.04"
             ]

releasenotes/notes/remove-debian-9-d083554a3b5d732f.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    Debian 9 support has been removed.