imap-send: use server conf argument in setup_curl()

imap-send: use server conf argument in setup_curl()

Our caller passes in an imap_server_conf struct, but we ignore it
totally, and instead read the config directly from the global "server"
variable. This works OK, since our sole caller will pass in that same
global variable. But the intent seems to have been to use the passed-in
variable, as otherwise it has no purpose (and many other functions use
the same pattern).

Let's use the passed-in value, which also silences a -Wunused-parameter
warning.

It would be nice if "server" was not a global here, as we could avoid
making similar mistakes. But changing that would be a larger refactor,
as it must be accessed as a global in a few spots (e.g., filling it in
with the config callback).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>