Replace json marshaler for x509 with custom impl (remove dependency)

[dopey]

zcrypto is being used to marshal x509 for certificate inspect. However, modifications were necessary to make zcrypto/x509 support *25519 keys. The CLI's using multiple version of crypto/x509 for various reasons in the codebase. Let's consider writing a custom implementation of JSON marshaling or integrate the functionality into a version of x509 in some other way.