Make test `CApiTest.RequestLoadCancellation` deterministic (#24348)
### Description
<!-- Describe your changes. -->
Make test `CApiTest.RequestLoadCancellation` deterministic by removing
the `terminator` thread.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
The test contributes to CI failures