MyFirstObjectWalk: fix description for counting omitted objects
Before the changes to count omitted objects, the function
traverse_commit_list() was used and its call cannot be changed to pass
a pointer to an oidset to record omitted objects.
Fix the text to clarify that we now use another traversal function to
be able to pass the pointer to the introduced oidset.
Helped-by: Kyle Lippincott <spectral@google.com>
Signed-off-by: Dirk Gouders <dirk@gouders.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>