Remove default_language from config.json

Specifying a default_language in the config might lead users to accidentally use the wrong language adapter.

config.json

@@ -9,7 +9,6 @@
   "attention_probs_dropout_prob": 0.1,
   "bos_token_id": 0,
   "classifier_dropout": null,
-  "default_language": "de_CH",
   "eos_token_id": 2,
   "hidden_act": "gelu",
   "hidden_dropout_prob": 0.1,