[Test] StartEventPipeSessionWithoutStackwalkTestAsync fails with ServerNotAvailableException

Re-enable this test after it is fixed.

Configuration: Ubuntu x64 Release

Error Message: `Microsoft.Diagnostics.NETCore.Client.ServerNotAvailableException : Could not send Stop command. The target process may have exited.`

Stack Trace:
```
at Microsoft.Diagnostics.NETCore.Client.EventPipeSession.Stop() in /__w/1/s/src/Microsoft.Diagnostics.NETCore.Client/DiagnosticsClient/EventPipeSession.cs:line 72
at Microsoft.Diagnostics.NETCore.Client.EventPipeSessionTests.StartEventPipeSessionWithoutStackwalkTestAsync(TestConfiguration testConfig) in /__w/1/s/src/tests/Microsoft.Diagnostics.NETCore.Client/EventPipeSessionTests.cs:line 223
at Microsoft.Diagnostics.NETCore.Client.EventPipeSessionTests.StartEventPipeSessionWithoutStackwalkTestAsync(TestConfiguration testConfig) in /__w/1/s/src/tests/Microsoft.Diagnostics.NETCore.Client/EventPipeSessionTests.cs:line 240
--- End of stack trace from previous location ---
```

Builds:
https://dev.azure.com/dnceng-public/public/_build/results?buildId=699794&view=ms.vss-test-web.build-test-results-tab&runId=17415602&resultId=100271&paneView=debug
https://dev.azure.com/dnceng-public/public/_build/results?buildId=697417&view=ms.vss-test-web.build-test-results-tab&runId=17348846&resultId=100271&paneView=debug