imap-send: remove useless uid code

imap-send: remove useless uid code

The imap-send code is based on code from isync, a program
for syncing imap mailboxes. Because of this, it has
inherited some code that makes sense for isync, but not for
imap-send.

In particular, when storing a message, it does one of:

  - if the server supports it, note the server-assigned
    unique identifier (UID) given to each message

  - otherwise, assigned a random UID and store it in the
    message header as X-TUID

Presumably this is used in isync to be able to synchronize
mailstores multiple times without duplication. But for
imap-send, the values are useless; we never do anything
with them and simply forget them at the end of the program.

This patch removes the useless code. Not only is it nice for
maintainability to get rid of dead code, but the removed
code relied on the existence of /dev/urandom, which made it
a portability problem for non-Unix platforms.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>