patch 8.2.3218: when using xchaha20 crypt undo file is not removed

Problem:    When using xchaha20 crypt undo file is not removed.
Solution:   Reset 'undofile' and delete the file. (Christian Brabandt,
            closes #8630, closes #8467)
diff --git a/src/crypt.c b/src/crypt.c
index 1b2ece5..fad6df0 100644
--- a/src/crypt.c
+++ b/src/crypt.c
@@ -616,11 +616,8 @@
 	// swap and undo files, so disable them
 	mf_close_file(curbuf, TRUE);	// remove the swap file
 	set_option_value((char_u *)"swf", 0, NULL, OPT_LOCAL);
-#ifdef FEAT_PERSISTENT_UNDO
-	set_option_value((char_u *)"udf", 0, NULL, OPT_LOCAL);
-#endif
 	msg_scroll = TRUE;
-	msg(_("Note: Encryption of swapfile not supported, disabling swap- and undofile"));
+	msg(_("Note: Encryption of swapfile not supported, disabling swap file"));
     }
 }
 #endif