Delete Mono build job (#7127)

Author: rainersigwald

.vsts-dotnet-ci.yml

@@ -228,47 +228,6 @@ jobs:
     continueOnError: true
     condition: always()
 
-- job: MonoOnMac
-  # Mono CI disabled until it can parse C# 9 syntax: https://github.com/dotnet/msbuild/issues/6058
-  condition: eq(1,2)
-  displayName: "macOS Mono"
-  pool:
-    vmImage: 'macOS-10.14'
-  steps:
-  # https://docs.microsoft.com/en-us/azure/devops/pipelines/agents/hosted?view=azure-devops&tabs=yaml#mono
-  - bash: |
-      SYMLINK=6_4_2
-      MONOPREFIX=/Library/Frameworks/Mono.framework/Versions/$SYMLINK
-      echo "##vso[task.setvariable variable=DYLD_FALLBACK_LIBRARY_PATH;]$MONOPREFIX/lib:/lib:/usr/lib:$DYLD_LIBRARY_FALLBACK_PATH"
-      echo "##vso[task.setvariable variable=PKG_CONFIG_PATH;]$MONOPREFIX/lib/pkgconfig:$MONOPREFIX/share/pkgconfig:$PKG_CONFIG_PATH"
-      echo "##vso[task.setvariable variable=PATH;]$MONOPREFIX/bin:$PATH"
-    displayName: Use Mono 6.4.2
-  - bash: 'eng/cibuild_bootstrapped_msbuild.sh --host_type mono /p:SuppressLicenseValidation=true'
-    displayName: CI Build
-  - task: PublishTestResults@2
-    displayName: Publish Mono Test Results
-    inputs:
-      testRunTitle: 'macOS Mono'
-      testRunner: XUnit
-      testResultsFiles: 'artifacts/TestResults/Debug-MONO/*UnitTests*.xml'
-      publishRunAttachments: true
-      mergeTestResults: true
-    continueOnError: true
-    condition: always()
-  - task: PublishBuildArtifacts@1
-    displayName: 'Publish Artifact: logs'
-    inputs:
-      PathtoPublish: 'artifacts/log'
-      ArtifactName: 'MonoOnMac build logs'
-    condition: always()
-  - task: PublishBuildArtifacts@1
-    displayName: 'Publish Artifact: TestResults'
-    inputs:
-      PathtoPublish: 'artifacts/TestResults'
-      ArtifactName: 'MonoOnMac test logs'
-    continueOnError: true
-    condition: always()
-
 - template: /eng/common/templates/job/source-build.yml
   parameters:
     platform: