Switch to libossp-uuid, to get UUIDs on Windows

This was only used to avoid a necessary check in collab builds on
Windows. @jtanx, who does the Windows binaries, says collab currently
isn’t building on Windows anyway.
This seems quite messy. The top of czmq/zuuid has a declaration which we may want to use instead of the raw 16. I don't see the size of a uuid changing (almost by definition) but its probably cleaner to not directly sprinkle that into the code.

    #define ZUUID_LEN    16