rm default model in .env.example [skip ci]

Author: erhant

.env.example

@@ -6,7 +6,8 @@ DKN_WALLET_SECRET_KEY=
 # You don't need to change this, simply copy and paste it.
 DKN_ADMIN_PUBLIC_KEY=0208ef5e65a9c656a6f92fb2c770d5d5e2ecffe02a6aade19207f75110be6ae658
 # model1,model2,model3,... (comma separated, case-insensitive)
-DKN_MODELS=phi3:3.8b
+# example: phi3:3.8b,gpt-4o-mini
+DKN_MODELS=
 
 ## DRIA (optional) ##
 # P2P address, you don't need to change this unless you really want this port.