string-list.[ch]: remove string_list_init() compatibility function

string-list.[ch]: remove string_list_init() compatibility function

Remove this function left over to accommodate in-flight changes, see
770fedaf9fb (string-list.[ch]: add a string_list_init_{nodup,dup}(),
2021-07-01) for the recent change to add
"string_list_init_{nodup,dup}()" initializers.

There was only one user of the API left in remote-curl.c. I don't know
why I didn't include this change to remote-curl.c in
bc40dfb10a0 (string-list.h users: change to use *_{nodup,dup}(),
2021-07-01), perhaps I just missed it.

In any case, let's change that one user to use the new API, as of
writing this there are no in-flight changes that use, so this seems
like a good time to drop this before we get any new users of this
compatibility API.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>