Revert "debian/control: build-dep on libldns-dev >= 1.6.13~"
Revert "debian/control: build-dep on libldns-dev >= 1.6.13~"

This reverts commit e8e8cc173c17091465cfbfcb7a5b8ea76d461b01.

stasic/debian-unbound,stasic/debian-unbound,stasic/debian-unbound,stasic/debian-unbound