merge-ort: drop unnecessary show_all_errors from collect_merge_info()

merge-ort: drop unnecessary show_all_errors from collect_merge_info()

collect_merge_info() has set info.show_all_errors = 1 since
d2bc1994f363 (merge-ort: implement a very basic collect_merge_info(),
2020-12-13).  This setting was copied from unpack-trees.c where it
controls batching of error messages for porcelain display, but
merge-ort has no such error-batching logic and never needed it.

With show_all_errors set, traverse_trees() captures a negative callback
return but continues processing remaining entries rather than stopping
immediately.  Removing the setting restores the default behavior where
a negative return from collect_merge_info_callback() breaks out of the
traversal loop right away, allowing a future commit to exit early when
a corrupt tree is detected.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>