ls-remote.txt: delete unsupported option

-u <exec> has never been supported, but it was mentioned since
0a2bb55 (git ls-remote: make usage string match manpage -
2008-11-11). Nobody has complained about it for seven years, it's
probably safe to say nobody cares. So let's remove "-u" in documents
instead of adding code to support it.

While at there, fix --upload-pack syntax too.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/ls-remote.c

@@ -4,7 +4,7 @@
 #include "remote.h"
 
 static const char ls_remote_usage[] =
-"git ls-remote [--heads] [--tags]  [-u <exec> | --upload-pack <exec>]\n"
+"git ls-remote [--heads] [--tags]  [--upload-pack=<exec>]\n"
 "                     [-q | --quiet] [--exit-code] [--get-url] [<repository> [<refs>...]]";
 
 /*