Wireshark doesn't use MySQL or any other SQL backend. I'm not sure what sort of dependency chain would trigger the installation of MySQL but it's unusual to say the least.
Almost certainly a packaging error where Wireshark depends on Qt and Qt includes all modules, including QtSql.
Looking at the exherbo package list, it seems that the qt4 package has an optional (or opportunistic) dependency on mysql. And on sqlite. So it ought to be possible to do the equivalent of an `apt-get install --no-install-recommends` to get it without mysql.