Fix the coverage build
Fix the coverage build

It was broken by temporarily duplicating the packaging of the PPX and
Camlp4 syntax, leading to duplicate rule generation in Jbuilder.

See

  80a2697273acc4da532f6feadd69ee3f9ec52ca3 (Camlp4)
  1ac67a58c9256fb4defc7842da326cfd6442f03b (PPX)

rneswold/lwt,c-cube/lwt,c-cube/lwt,ocsigen/lwt,ocsigen/lwt,c-cube/lwt,rneswold/lwt,rneswold/lwt,ocsigen/lwt