*: replace deprecated free_commit_list

*: replace deprecated free_commit_list

Replace `free_commit_list` with `commit_list_free`. The former was
deprecated in 9f18d089 (commit: rename `free_commit_list()` to conform
to coding guidelines, 2026-01-15).

This allows us to remove all the deprecated functions in the
next commit:

• `copy_commit_list`
• `reverse_commit_list`
• `free_commit_list`

Acked-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>