### Description
BUG FIX: the if...else in telemetry-steps.yml does not really work. It
always says "Telemetry is disabled." even through the pipeline doesn't
have the pipeline variable.
### Motivation and Context
For example, recently I setup a new pipeline in
https://dev.azure.com/onnxruntime/onnxruntime/_build without setting the
ADO variable, but the powershell code still thinks that we have enabled
telemetry.
See:
https://dev.azure.com/onnxruntime/onnxruntime/_build/results?buildId=910107&view=results
The reason it didn't work because when the pipeline
variable("TELEMETRYGUID") doesn't exist, the occurrence of
"$(TELEMETRYGUID)" would be not replace to anything. It will remain as
it is.
