perldelta for ae78ae4, smart match removal

pod/perldelta.pod

@@ -45,6 +45,19 @@ XXX For a release on a stable branch, this section aspires to be:
 
 [ List each incompatible change as a =head2 entry ]
 
+=head2 Switch and Smart Match operator removed
+
+The "switch" feature and the smartmatch operator, C<~~>, were introduced in
+v5.10.  Their behavior was significantly changed in v5.10.1.  When the
+"experiment" system was added in v5.18.0, switch and smartmatch were
+retroactively declared experimental.  Over the years, proposals to fix or
+supplement the features have come and gone.
+
+They were deprecated in Perl v5.38.0 and scheduled for removal in Perl
+5.42.0
+
+These features have now been entirely removed.
+
 =head1 Deprecations
 
 XXX Any deprecated features, syntax, modules etc. should be listed here.