chore: remove deprecated GitHub Actions SonarQube workflow

SonarQube scan is already being run in the final_job of CircleCI
pipeline, which collects coverage from all test jobs and reports to
the current SonarQube server.

The GitHub Actions workflow was sending scan reports to a deprecated
SonarQube server, creating duplicate scans and unnecessary overhead.

Signed-off-by: Arjun Rajappa <arjun.rajappa@ibm.com>

Author: arjun-rajappa