Cleanup symlinks before running acme.sh

acme.sh copies the ssl cert to the ssl cert folder of the website or to the ispconfig folder instead of symlinking it. When a setup is switched from certbot to acme.sh, then acme.sh will write its certs trough the existing certbot symlinks to /etc/letsencrypt/ instead of writing the file to the ssl folder of the website or the global ssl folder. To avoid that, the symlinks in the ssl folders should be removed before executing acme.sh.