ci: remove CodeQL workflow in favour of GHAS default setup

The workflow at .github/workflows/codeql.yaml was the stock 'advanced
setup' template with no customisation (no custom query suite, no
config file, no path filters, no manual build steps). It produces the
same analysis coverage as GHAS default setup for JavaScript/TypeScript
and Python, but requires us to maintain the workflow, pin action SHAs
and follow major-version bumps of github/codeql-action.

Switching to default setup removes that maintenance burden. Activation
steps are listed in the PR description.

Author: einarwar