Remove links to v13 wiki

Extensions---Your-first-Bot.md

@@ -1,5 +1,3 @@
-> ⚠️ This is the v20.x version of the wiki. For the v13.x version, please [head to the v13.x wiki](https://github.com/python-telegram-bot/v13.x-wiki/wiki).
-
 ## Introduction
 The `telegram.ext` submodule is built on top of the pure API implementation. It provides an easy-to-use interface and takes some work off the programmer, so you [don't have to repeat yourself](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself).
 

Home.md

@@ -1,7 +1,5 @@
 [![Logo](https://github.com/python-telegram-bot/logos/raw/master/logo-text/png/ptb-logo-text_768.png)](https://python-telegram-bot.org/)
 
-# ⚠️ This is the v20.x version of the wiki. For the v13.x version, please head [here](https://github.com/python-telegram-bot/v13.x-wiki/wiki).
-
 ## PTB Resources
 
 PTB offers different resources that help you understand and use the features of the library.

Introduction-to-the-API.md

@@ -1,5 +1,3 @@
-> ⚠️ This is the v20.x version of the wiki. For the v13.x version, please [head to the v13.x wiki](https://github.com/python-telegram-bot/v13.x-wiki/wiki).
-
 ## Pure Telegram Bot API
 
 The Bot API is exposed via the [`telegram.Bot`](https://python-telegram-bot.readthedocs.io/telegram.bot.html) class.

_Sidebar.md

@@ -1,5 +1,3 @@
-# ⚠️ This is the v20.x version of the wiki. For the v13.x version, please head [here](https://github.com/python-telegram-bot/v13.x-wiki/wiki).
-
 ## Must read
 
 1. [[Introduction to the API|Introduction-to-the-API]]