fix: remove system-default-registry flag from k3s and rke2

Author: pratikjagrut

channels-rke2.yaml

@@ -120,8 +120,6 @@ releases:
         type: bool
       audit-policy-file:
         type: string
-      system-default-registry:
-        type: string
       protect-kernel-defaults:
         type: boolean
         default: false

channels.yaml

@@ -165,8 +165,6 @@ releases:
     serverArgs: *serverArgs-v2
     agentArgs: &agentArgs-v2
       <<: *agentArgs-v1
-      system-default-registry:
-        type: string
   - version: v1.21.10+k3s1
     minChannelServerVersion: v2.6.3-alpha1
     maxChannelServerVersion: v2.6.4