patch 8.1.1479: change included for debugging only

Problem:    Change included for debugging only.
Solution:   Restore the REDIR_TEST_TO_NULL line.
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index 4bfc400..f28c941 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -12,7 +12,7 @@
 # Comment out this line to see the verbose output of tests.
 #
 # Catches SwapExists to avoid hanging at the ATTENTION prompt.
-# REDIR_TEST_TO_NULL = --cmd 'au SwapExists * let v:swapchoice = "e"' > /dev/null
+REDIR_TEST_TO_NULL = --cmd 'au SwapExists * let v:swapchoice = "e"' > /dev/null
 
 # Uncomment this line to use valgrind for memory leaks and extra warnings.
 #   The output goes into a file "valgrind.testN"