sync bin_prot 0.17.0 opam

[olafhering]

For some reason janestreet/bin_prot#29 was not merged with d87bb8f.

I'm not familiar with opam, this may have been done with purpose. In case this was just an oversight, commit 5c8da83 is probably obsolete as well.

[raphael-proust]

pinging @dkalinichenko-js who might have an answer about intentionality

[dkalinichenko-js]

Hi! It looks like that PR was merged after the v0.17 release was finished. It'll be included in the next release.