Remove echo when a dead SSH Agent PID is found

This case can be safely ignored, no need to print a message for that.

Fixes #1579

plugins/available/sshagent.plugin.bash

@@ -94,7 +94,6 @@ function _ensure_valid_sshagent_env() {
     return
   fi
 
-  echo "There's a dead ssh-agent at the landing..."
   ssh-agent > "${SSH_AGENT_ENV}"
   return
 }