Remove dead code which contains bad gettext block

Found this dead code when I examine gettext messages in shell scripts
start with dash ('-' or '--'). An error will be raised for this case,
like:

    $ gettext "-d option is no longer supported.  Do not use."
    gettext: missing arguments

Indead, this code has been left as dead for a long time, as Jonathan
points out:

    The git am -d/--dotest option has errored out with a message
    since e72c740 (am: remove support for -d .dotest, 2008-03-04).
    The error message about lack of support was eliminated along
    with other cleanups (probably by mistake) a year later by
    removing the option from the option table in 98ef23b (git-am:
    minor cleanups, 2009-01-28).

    But the code to handle -d and --dotest stayed around even though
    ever since then it could not be tripped.  Remove this dead code.

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

git-am.sh

@@ -413,9 +413,6 @@ it will be removed. Please do not use it anymore."
 		abort=t ;;
 	--rebasing)
 		rebasing=t threeway=t ;;
-	-d|--dotest)
-		die "$(gettext "-d option is no longer supported.  Do not use.")"
-		;;
 	--resolvemsg)
 		shift; resolvemsg=$1 ;;
 	--whitespace|--directory|--exclude|--include)