patch 8.2.2613: new test throws exception

Problem:    New test throws exception.
Solution:   Adjust the function cleanup.
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index f76718f..741e315 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -504,7 +504,7 @@
   bwipe!
   unlet g:exprLine
   unlet g:exprCol
-  delfunc ExprMapped
+  delfunc StoreColumn
   nunmap x
   nunmap !
 endfunc