dnssec-conf: remove raw manpages

dnssec-conf builds manpages using xmlto.  Remove the raw manpages and add
a dependency on xmlto-native to support building the manapages from the
actual source.

Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>