The GPG key for the APT repository has expired, causing apt update to fail. Removing the apt repo fixes the issue as we don't need the repo.

Proposed commit message

    metricbeat: remove mongodb apt repo from integration test docker image
    
    The GPG key for the APT repository has expired, causing apt update to fail.
    Removing the apt repo fixes the issue as we don't need the repo.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files
• [ ] I have added tests that prove my fix is effective or that my feature works. Where relevant, I have used the stresstest.sh script to run them under stress conditions and race detector to verify their stability.
• [ ] I have added an entry in ./changelog/fragments using the changelog tool.

Disruptive User Impact

None

How to test this PR locally

cd metricbeat/module/mongodb/_meta
docker build -t docker.elastic.co/integrations-ci/beats-mongodb .

the build should succeed

Related issues

• N/A