Fix recursive json object created in mention parsing (#2334)

src/main/java/net/dv8tion/jda/internal/entities/MessageMentionsImpl.java

@@ -57,7 +57,7 @@ public MessageMentionsImpl(JDAImpl jda, GuildImpl guild, String content,
                     }
 
                     DataObject member = obj.getObject("member");
-                    obj.remove("user");
+                    obj.remove("member");
                     member.put("user", obj).put("is_member", true);
                     this.userMentionMap.put(obj.getUnsignedLong("id"), member);
                 });