ppx-sexp-conv is marked for autoremoval from testing

[Debian testing autoremoval watch]

ppx-sexp-conv 113.33.03-2 is marked for autoremoval from testing on 2017-11-08

It (build-)depends on packages with these RC bugs:
876725: ppx-deriving: ppx-deriving FTBFS with OCaml 4.05.0