Bump xmlhttprequest-ssl and karma

Removes [xmlhttprequest-ssl](https://github.com/mjwwit/node-XMLHttpRequest). It's no longer used after updating ancestor dependency [karma](https://github.com/karma-runner/karma). These dependencies need to be updated together.


Removes `xmlhttprequest-ssl`

Updates `karma` from 4.4.1 to 6.4.2
- [Release notes](https://github.com/karma-runner/karma/releases)
- [Changelog](https://github.com/karma-runner/karma/blob/master/CHANGELOG.md)
- [Commits](karma-runner/karma@v4.4.1...v6.4.2)

---
updated-dependencies:
- dependency-name: xmlhttprequest-ssl
  dependency-type: indirect
- dependency-name: karma
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>