Remove some unneeded build deps
    
    ... that were added in commit c038f5e5b56d657cfc7ba32446de11df2b37b61b
    without any explanation. gnome-icon-theme build doesn't need the header
    files from gtk2-devel and librsvg2-devel and only needs the base
    packages -- the gtk2 build dep is solely for
    /usr/bin/gtk-update-icon-cache.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=972372#c9