graphics/llpp: Mark as broken and deprecate

llpp fails to build after r493732. llpp >= 30 should support MuPDF
1.14.0 out of the box however it needs a newer Ocaml compiler > 4.07.
Previously I have backported some changes to support a newer
MuPDF, but this is not trivial this time. The lang/ocaml update
has been stalled for years now and at this point I give up.