improve wording of one-to-one-chat hint (#2165)

* improve wording of one-to-one-chat hint

at #2134 we shortend the hint shown for an empty group massively,
removing greylisting hints and the hint that the recipient can user other mua.

the result of that shortening is that the creation of a one-to-one chat
is now way too long :)

i suggest shorten the hint in a similar way,
not much would be left then, however, that is maybe not bad :)

* re-add the aspect that the recipient does not need Delta Chat

src/org/thoughtcrime/securesms/ConversationFragment.java

@@ -191,7 +191,7 @@ public class ConversationFragment extends MessageSelectorFragment
             noMessageTextView.setText(R.string.device_talk_explain);
         }
         else {
-            String message = getString(R.string.chat_no_messages_hint, dcChat.getName(), dcChat.getName());
+            String message = getString(R.string.chat_new_one_to_one_hint, dcChat.getName());
             noMessageTextView.setText(message);
         }
     }