Fix gpg-agent plugin checks (#6469)

* Always try and start gpg-agent, with --use-standard-socket it will try and use a standard socket directory. It won't start multiple agents if agent is already running. In addition, XDG_RUNTIME_DIR isn't always set

* ssh socket if broken if --daemon is run again, so onky start if we don't have a socket

* Removed unnecessary allocation of GPG_SSH_AUTH_SOCK