refactor: delete commented-out function bodies

Three large dead-code blocks removed:

- 16-line commented-out org-drill-entry-due-p (replaced by current
  implementation that takes a session arg)
- 17-line commented-out org-drill-hide-all-subheadings-except (the
  body was a placeholder docstring + commented body; the real
  function lives elsewhere now)
- 25-line block of commented-out alternative
  org-drill-add-cloze-fontification + add-hook XXX commentary

Pure deletion, no behavior change.  Version control has the history.

0 files changed, 0 insertions, 0 deletions