add deleteChatPhoto method

bot.go

@@ -934,3 +934,15 @@ func (bot *BotAPI) SetChatPhoto(config SetChatPhotoConfig) (APIResponse, error)
 
 	return bot.UploadFile(config.method(), params, config.name(), file)
 }
+
+// DeleteChatPhoto delete photo of chat.
+func (bot *BotAPI) DeleteChatPhoto(config DeleteChatPhotoConfig) (APIResponse, error) {
+	v, err := config.values()
+	if err != nil {
+		return APIResponse{}, err
+	}
+
+	bot.debugLog(config.method(), v, nil)
+
+	return bot.MakeRequest(config.method(), v)
+}

configs.go

@@ -1126,3 +1126,20 @@ func (config SetChatPhotoConfig) name() string {
 func (config SetChatPhotoConfig) method() string {
 	return "setChatPhoto"
 }
+
+// DeleteChatPhotoConfig contains information for delete chat photo.
+type DeleteChatPhotoConfig struct {
+	ChatID int64
+}
+
+func (config DeleteChatPhotoConfig) method() string {
+	return "deleteChatPhoto"
+}
+
+func (config DeleteChatPhotoConfig) values() (url.Values, error) {
+	v := url.Values{}
+
+	v.Add("chat_id", strconv.FormatInt(config.ChatID, 10))
+
+	return v, nil
+}