py3: use "%d" % val for int rather than pycompat.bytestr
Earlier I used pycompat.bytestr() to convert integers to bytes, but we can do
b"%d" % val to convert that int to bytes. b'' is already added by the
transformer.
Thanks to Yuya for suggesting this.
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors