Remove unnecessary access token variable.

Author: mijpeterson

.github/workflows/pr-azure-pipelines.yml

@@ -72,8 +72,6 @@ extends:
           # 1ES PT requires explicit build task for Roslyn analysis. Auto-injected Roslyn task will use build logs from this build.
           - task: DotNetCoreCLI@2
             displayName: Build projects
-            env:
-              ADO_TOKEN: $(System.AccessToken)
             inputs:
               command: 'build'
               arguments: --no-restore