package/dovecot: security bump to version 2.3.4

Fixes CVE-2017-15130, CVE-2017-14461 & CVE-2017-15132:
https://www.dovecot.org/list/dovecot-news/2018-February/000370.html

Removed patch applied upstream:
https://github.com/dovecot/core/commit/a008617e811673064fd657acf517dc4a12493d29



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