t2004: drop unnecessary write-tree/read-tree

Unlike earlier tests which reference several trees prepared by "setup",
no other tests utilize the tree from the "symlink" test, so there is no
need to write it (or read it back immediately).

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: sunshineco

t/t2004-checkout-cache-temp.sh

@@ -198,9 +198,6 @@ test_expect_success 'checkout --temp within subdir' '
 test_expect_success 'checkout --temp symlink' '
 	rm -f path* .merge_* actual .git/index &&
 	test_ln_s_add b a &&
-	t4=$(git write-tree) &&
-	rm -f .git/index &&
-	git read-tree $t4 &&
 	git checkout-index --temp -a >actual &&
 	test_line_count = 1 actual &&
 	test $(cut "-d	" -f2 actual) = a &&