security/cryptopp: Update to 8.4.0
Bump PORTREVSION on all consumers. ABI-breaking changes were introduced and
recompile of consumers is necessary.
Remove unused cryptopp dependency from devel/xeus. Upstream migrated to OpenSSL
several releases ago. [1]
[1] https://github.com/jupyter-xeus/xeus/commit/c98c44c174cafcf424f4203dc3c61564118feb3e