Removal of unnecessary forked repositories

[cipherboy]

The following plugin repositories are built-in plugins in OpenBao and thus did not need to be forked:

• https://github.com/openbao/openbao-plugin-auth-jwt
• https://github.com/openbao/openbao-plugin-secrets-kubernetes
• https://github.com/openbao/openbao-plugin-auth-kubernetes
• https://github.com/openbao/openbao-plugin-auth-kerberos
• https://github.com/openbao/openbao-plugin-secrets-openldap
• https://github.com/openbao/openbao-plugin-secrets-kv

This list can be verified through these two listings:

• openbao-plugin-auth-* from builtin/credential
• openbao-plugin-secret-* from builtin/logical

IMO, the remaining plugins of upstream could be used verbatim unless we wish to modify them; at which point they could be forked.

/cc @naphelps