[Internal] Remove downstream testing workflows (#904)

## What changes are proposed in this pull request?

This PR removes the downstream workflows. Results from these workflows
have been ignored for the last quarters and create confusion to
contributors. Downstream tests that are relevant to validate the SDK
will be moved either to the actual integration tests or as unit tests.

## How is this tested?

N/A

NO_CHANGELOG=true

Author: renaudhartert-db