remove 2.21

Author: mongoKart

source/whats-new.txt

@@ -15,7 +15,7 @@ What's New
    :values: reference
 
 .. meta::
-   :keywords: update, new feature, deprecation, upgrade, driver v2.19, driver v2.20, driver v2.21, driver v2.22, driver v2.23, driver v2.24, driver v2.25, driver v2.26, driver v2.27, driver v2.28, driver v3.0
+   :keywords: update, new feature, deprecation, upgrade, driver v2.22, driver v2.23, driver v2.24, driver v2.25, driver v2.26, driver v2.27, driver v2.28, driver v3.0
 
 Learn what's new in:
 
@@ -29,7 +29,6 @@ Learn what's new in:
 * :ref:`Version 2.24 <version-2.24>`
 * :ref:`Version 2.23 <version-2.23>`
 * :ref:`Version 2.22 <version-2.22>`
-* :ref:`Version 2.21 <version-2.21>`
 
 .. _upcoming-breaking-changes: