Remove dead symbolic links

for i in `find .`; do if (test -h $i); then file $i|grep broken; fi; done

./es/99book.bib: broken symbolic link to `../en/99book.bib'
./es/bookhtml.cfg: broken symbolic link to `../en/bookhtml.cfg'
./es/fixhtml.py: broken symbolic link to `../en/fixhtml.py'
./es/hgbook.css: broken symbolic link to `../en/hgbook.css'
./es/htlatex.book: broken symbolic link to `../en/htlatex.book'