Editorial change: remove deprecated command-line switches

Author: gusthoff

content/courses/whats-new-in-ada-2022/chapters/introduction.rst

@@ -10,10 +10,7 @@ in GNAT Ada compiler.
 To use some of these features, you may need to use a compiler command
 line switch or pragma. Compilers starting with `GNAT Community Edition
 2021`_ or `GCC 11`_ use :ada:`pragma Ada_2022;` or the ``-gnat2022``
-switch.  Older compilers use :ada:`pragma Ada_2020;` or
-``-gnat2020``. To use the square brackets syntax or :ada:`'Reduce`
-expressions, you need :ada:`pragma Extensions_Allowed (On);` or the
-``-gnatX`` switch.
+switch.
 
 References
 ----------