stash: remove now superfluos help for "stash push"

stash: remove now superfluos help for "stash push"

With the 'git stash save' interface, it was easily possible for users to
try to add a message which would start with "-", which 'git stash save'
would interpret as a command line argument, and fail.  For this case we
added some extra help on how to create a stash with a message starting
with "-".

For 'stash push', messages are passed with the -m flag, avoiding this
potential pitfall.  Now only pathspecs starting with "-" would have to
be distinguished from command line parameters by using
"-- --<pathspec>".  This is fairly common in the git command line
interface, and we don't try to guess what the users wanted in the other
cases.

Because this way of passing pathspecs is quite common in other git
commands, and we don't provide any extra help there, do the same in the
error message for 'git stash push'.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>