tests: Don’t check for libdl on FreeBSD or NetBSD either
tests: Don’t check for libdl on FreeBSD or NetBSD either

As with commit c14ac90ed2347ef050ccc83ef6b7b183cec6d0e4, it isn’t needed
and doesn’t exist.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #1739

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib