chore: remove temporary documentation files

Remove RELEASE_FIX_SUMMARY.md and SQUASH_MERGE_SETUP.md as the
information has been incorporated into permanent documentation:
- .github/CONTRIBUTING.md has commit type guidelines
- .github/SQUASH_MERGE.md has squash merge instructions
- tracking/documentation.md has the complete history

These temporary files served their purpose during troubleshooting.

Author: tip-dteller