rebase-interactive: re-word "item count" comment

rebase-interactive: re-word "item count" comment

97f05f43 (Show number of TODO items for interactive rebase, 2014-12-10)
taught rebase-interactive to display an item count in the instruction
list comments:

    # Rebase 46640c6..5568fd5 onto 46640c6 (4 TODO item(s))
    #
    # Commands:
    # p, pick = use commit
    # ...

However, with the exception of the --edit-todo option, "TODO" is a
one-off term, never presented to the user by rebase-interactive in
any other context. The item count is in fact the number of commands
("pick", "edit", etc.) remaining on the instruction sheet, and the
comment immediately following it talks about "Commands". Consequently,
replace "(# TODO item(s))" with the more accurate and meaningful
"(# command(s))".

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>