package/dovecot: needs OpenSSL

package/dovecot: needs OpenSSL

The latest version bump to 2.27 introduced a bug in the configure
script which occurs when OpenSSL support is missing:
http://lists.busybox.net/pipermail/buildroot/2016-December/179397.html

This patch makes OpenSSL mandatory following the upstream advice:
http://www.dovecot.org/list/dovecot/2016-December/106346.html
"Nobody really should be building without OpenSSL nowadays anyway"

Fixes
http://autobuild.buildroot.net/results/85f/85f2f176c108ab36520f02d975f27c27cddce84b/

[Peter: drop legacy handling]
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>