Minimal ZTS: Remove workflows and comment out non-L2ARC tests

- Remove GitHub workflow files (checkstyle, codeql, labels, zloop)
- Reduce common.run to only L2ARC tests (10-15 min vs 4-5 hours)
- Comment out non-L2ARC tests in linux.run and freebsd.run (preserving structure)
- Compatible with GitHub Actions for fast L2ARC testing

Signed-off-by: Ameer Hamza <[email protected]>

Author: ixhamza