Remove dead symbol server PAT group

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mmitche

azure-pipelines-official.yml

@@ -67,8 +67,6 @@ variables:
     - name: Codeql.Cadence 
       value: 0
 
-  - group: DotNet-Symbol-Server-Pats
-
 resources:
   repositories:
   - repository: 1ESPipelineTemplates