Nyxt: Use *run-from-repl-p* instead of *keep-alive*.

.config/nyxt/slynk.lisp

@@ -10,5 +10,6 @@ before running this command."
   (echo "Slynk server started at port ~a" slynk-port))
 
 ;; Start slynk by default.
-(unless nyxt::*keep-alive*
+;; WARNING: This triggers an error if another instance is already running at 4006.
+(unless nyxt::*run-from-repl-p*
   (slynk:create-server :port 4006 :dont-close t))