Log Message:
Update to 1.6 from Jaap Boender in PR 46800:

This update of ocaml-cryptokit to its newest version, 1.6. does
not actually change anything in the functionality of the software.
Upstream, the build system has changed, and there are also a few
changes to the package (most notably, removal of the PLIST.opt in
favour of the PLIST_VARS system)