remove version field from opam file

4 jobs for master in 46 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
canceled stdpp-coq8.6 #3407
fp-timing

canceled stdpp-coq8.6.1 #3406
fp-timing

00:00:44

canceled stdpp-coq8.7 #3405
fp-timing

00:00:46

 
  Opam
canceled opam #3408