Stop creating wrong devel manual pages
    
    Devel manual pages install correct manual pages with 3.gz suffix. But
    there are also additional links just with .gz suffix. They are created
    only in spec file. I think they were needed before unbound contained
    proper installation of manuals for development. It is missing .3 suffix.
    But it is not necessary anymore, because such recipe already exists in
    upstream Makefile.in.
    
    Resolves: rhbz#2078929