[Ubuntu 22] Removing .Net version 6.0 (#12652)

Author: hemanthmanga

images/ubuntu/toolsets/toolset-2204.json

@@ -267,12 +267,10 @@
     ],
     "dotnet": {
         "aptPackages": [
-            "dotnet-sdk-6.0",
             "dotnet-sdk-8.0",
             "dotnet-sdk-9.0"
         ],
         "versions": [
-            "6.0",
             "8.0",
             "9.0"
         ],