Revert adding Illink arm tests (#3094)

Remove Illink arm tests and leave a comment clarifying why we are not running Illink on ARM machines.

azure-pipelines.yml

@@ -504,8 +504,7 @@ jobs:
       buildMachines:
         - win-x64
         - ubuntu-x64
-        - win-arm64
-        - ubuntu-arm64-ampere
+        # Illink.Utilities is not supported on ARM: The type initializer for 'ILLinkBenchmarks.Utilities' threw a NotSupportedException (Unsupported architecture). (06/2023)
       isPublic: false
       jobParameters:
         kind: illink