Remove --with-distro-version
    
    Remove support for "--with-distro-version" configure option as unused.
    
    The option was added in August 2011 (d3da1c1). As of now nothing seems
    to use it. Packaging checked: rpm, deb, pacman, ebuilds, FreeBSD ports.
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>