Revert "fix(db): fallback to CAR DB head when HEAD_KEY not set (#5223)"

[LesnyRumcajs]

This reverts commit d9e76f6.

Summary of changes

Changes introduced in this pull request:

• The HEAD changes (d9e76f6) are causing Forest to always require a snapshot. For example, running ❯ forest --chain calibnet --encrypt-keystore false --import-snapshot ../snapshots/calibnet , exiting and then ❯ forest --chain calibnet --encrypt-keystore false will result in download snapshot prompt.

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.