Remove outdated note in README (NFC)

Support for Python2 was dropped back in 2022 by 0e3a5f7 .

Remove outdated note in README.

Author: JOE1994

README.md

@@ -21,4 +21,4 @@ Testing
 =======
 
 Testing is done by running tox from the top-level directory. It runs the tests
-for both Python 2 and Python 3, it also checks code style.
+for Python 3 and checks code style.