fix: remove the reset-to-defaults button from tag settings

If you carefully crafted your tags and then click this button by accident, all
your hard work is gone. A confirmation message would be the other solution but
since I have difficulty to grasp when you would need such a button, I propose
to just remove it.

locales/ja/common.json

@@ -1016,7 +1016,6 @@
       "title": "メールラベル",
       "description": "メールをカラーで整理するためのラベルを定義します。サーバーにJMAPキーワードとして保存されます。",
       "add_keyword": "ラベルを追加",
-      "reset_defaults": "デフォルトに戻す",
       "label_field": "表示名",
       "label_placeholder": "例：仕事、個人、緊急",
       "id_field": "ラベルID",