submodule: inline submodule_commits() into caller
When collecting the string_list of changed submodule names, the new
submodules commits are stored in the string_list_item.util as an
oid_array. A subsequent commit will replace the oid_array with a struct
that has more information.
Prepare for this change by inlining submodule_commits() (which inserts
into the string_list and initializes the string_list_item.util) into its
only caller so that the code is easier to refactor later.
Signed-off-by: Glen Choo <chooglen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>