Remove AKS 1.19 from compatability matrix

At this moment, BKPR only supports k8s systems that use the docker CRI.
As of AKS 1.19, containerd is the only container runtime option.

Until further analysis on how we want to support containerd, we're
reducing the scope of compability for now.

Jenkinsfile

@@ -19,7 +19,7 @@ import org.jenkinsci.plugins.pipeline.modeldefinition.Utils
 // NOTE: need update below map at jenkins/cloud-custodian/Jenkinsfile
 // (until we create a common file for shared Jenkins code/data)
 def buildRelDefaults = [
-  'AKS_REL': '1.18,1.19',
+  'AKS_REL': '1.18',
   'EKS_REL': '1.18,1.19',
   'GKE_REL': '1.18,1.19',
   'GEN_REL': '1.18', // generic is tested on GKE stable channel

README.md

@@ -30,8 +30,7 @@ The following matrix shows which Kubernetes versions and platforms are supported
 | `1.6` (deprecated) | `1.15`-`1.16` | `1.15`-`1.16` | `1.15`-`1.16` |
 | `1.7`              | `1.16`-`1.17` | `1.16`-`1.17` | `1.16`-`1.17` |
 | `1.8` (current)    | `1.17`-`1.18` | `1.17`-`1.18` | `1.17`-`1.18` |
-| `1.9`  (planned)   | `1.18`-`1.19` | `1.18`-`1.19` | `1.18`-`1.19` |
-| `1.10` (planned)   | `1.19`-`1.20` | `1.19`-`1.20` | `1.19`-`1.20` |
+| `1.9` (planned)    | `1.18`        | `1.18`-`1.19` | `1.18`-`1.19` |
 
 Note that the (experimental) `generic` platform is e2e tested on GKE.