remove unused old videochat invitation API

src/main/java/com/b44t/messenger/DcContext.java

@@ -203,7 +203,6 @@ public class DcContext {
     public native boolean      resendMsgs           (int msg_ids[]);
     public native int          sendMsg              (int chat_id, DcMsg msg);
     public native int          sendTextMsg          (int chat_id, String text);
-    public native int          sendVideochatInvitation(int chat_id);
     public native boolean      sendWebxdcStatusUpdate(int msg_id, String payload);
     public native String       getWebxdcStatusUpdates(int msg_id, int last_known_serial);
     public native void         setWebxdcIntegration (String file);

src/main/java/com/b44t/messenger/DcMsg.java

@@ -154,8 +154,6 @@ public class DcMsg {
     public native boolean isInfo             ();
     public native boolean hasHtml            ();
     public native String  getSetupCodeBegin  ();
-    public native String  getVideochatUrl    ();
-    public native int     getVideochatType   ();
     public native void    setText            (String text);
     public native void    setFileAndDeduplicate(String file, String name, String filemime);
     public native void    setDimension       (int width, int height);