Update dnsdist to next major release 1.4.0. This release introduces
dependencies on libh2o-evloop and libwslay for support of DNS over
HTTPS.

Release Blog Post: https://blog.powerdns.com/2019/11/20/dnsdist-1-4-0/
Changelog: https://dnsdist.org/changelog.html#change-1.4.0

Also removes compatibility patches required for previous release that have
been incorporated upstream.

Signed-off-by: James Taylor <james@jtaylor.id.au>