rebase: remove obsolete and unused LONG_USAGE which breaks xgettext

Since there is a modern OPTIONS_SPEC variable in use in this script,
the obsolete USAGE and LONG_USAGE variables are no longer used.
Remove them.

In addition, the obsolete LONG_USAGE variable has the following
message in it:

    A'\''--B'\''--C'\''

And such complex LONG_USAGE message will break xgettext when
extracting l10n messages (but if single quotes are removed from the
message, xgettext works fine on 'git-rebase.sh').

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Reviewed-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -3,31 +3,6 @@
 # Copyright (c) 2005 Junio C Hamano.
 #
 
-USAGE='[--interactive | -i] [--exec | -x <cmd>] [-v] [--force-rebase | -f]
-       [--no-ff] [--onto <newbase>] [<upstream>|--root] [<branch>] [--quiet | -q]'
-LONG_USAGE='git-rebase replaces <branch> with a new branch of the
-same name.  When the --onto option is provided the new branch starts
-out with a HEAD equal to <newbase>, otherwise it is equal to <upstream>
-It then attempts to create a new commit for each commit from the original
-<branch> that does not exist in the <upstream> branch.
-
-It is possible that a merge failure will prevent this process from being
-completely automatic.  You will have to resolve any such merge failure
-and run git rebase --continue.  Another option is to bypass the commit
-that caused the merge failure with git rebase --skip.  To check out the
-original <branch> and remove the .git/rebase-apply working files, use the
-command git rebase --abort instead.
-
-Note that if <branch> is not specified on the command line, the
-currently checked out branch is used.
-
-Example:       git-rebase master~1 topic
-
-	A---B---C topic                   A'\''--B'\''--C'\'' topic
-       /                   -->           /
-  D---E---F---G master          D---E---F---G master
-'
-
 SUBDIRECTORY_OK=Yes
 OPTIONS_KEEPDASHDASH=
 OPTIONS_SPEC="\