t6418: tighten delete/normalize conflict testcase

The testcase only required that the merge complete without conflict,
without specifying what the correct resolution was.  Since normalization
changed this from a modify/delete to a not-modified/delete, the correct
resolution is to have the file be removed at the end.  Add a check for
this resolution.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6418-merge-text-auto.sh

@@ -197,7 +197,8 @@ test_expect_success 'Test delete/normalize conflict' '
 	git commit -m "remove file" &&
 	git checkout master &&
 	git reset --hard a^ &&
-	git merge side
+	git merge side &&
+	test_path_is_missing file
 '
 
 test_done