Removed outdated warning about prompt_toolkit 2.0 from docs.

Author: jonathanslenders

docs/index.rst

@@ -1,13 +1,6 @@
 Python Prompt Toolkit 3.0
 =========================
 
-.. warning::
-
-    Notice that this is the prompt_toolkit 3.0 documentation. It is mostly
-    compatible with the 2.0 branch. The difference is that prompt_toolkit 3.0
-    requires at least Python 3.6. On the plus side, it uses asyncio natively
-    (rather than it's own event loop), and we have type annotations everywhere.
-
 `prompt_toolkit` is a library for building powerful interactive command line
 and terminal applications in Python.