t5318: avoid unnecessary command substitutions

Two tests added in dade47c06c (commit-graph: add repo arg to graph
readers, 2018-07-11) prepare the contents of 'expect' files by
'echo'ing the results of command substitutions.  That's unncessary,
avoid them by directly saving the output of the commands executed in
those command substitutions.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5318-commit-graph.sh

@@ -444,25 +444,27 @@ test_expect_success 'setup non-the_repository tests' '
 test_expect_success 'parse_commit_in_graph works for non-the_repository' '
 	test-tool repository parse_commit_in_graph \
 		repo/.git repo "$(git -C repo rev-parse two)" >actual &&
-	echo $(git -C repo log --pretty="%ct" -1) \
-		$(git -C repo rev-parse one) >expect &&
+	{
+		git -C repo log --pretty=format:"%ct " -1 &&
+		git -C repo rev-parse one
+	} >expect &&
 	test_cmp expect actual &&
 
 	test-tool repository parse_commit_in_graph \
 		repo/.git repo "$(git -C repo rev-parse one)" >actual &&
-	echo $(git -C repo log --pretty="%ct" -1 one) >expect &&
+	git -C repo log --pretty="%ct" -1 one >expect &&
 	test_cmp expect actual
 '
 
 test_expect_success 'get_commit_tree_in_graph works for non-the_repository' '
 	test-tool repository get_commit_tree_in_graph \
 		repo/.git repo "$(git -C repo rev-parse two)" >actual &&
-	echo $(git -C repo rev-parse two^{tree}) >expect &&
+	git -C repo rev-parse two^{tree} >expect &&
 	test_cmp expect actual &&
 
 	test-tool repository get_commit_tree_in_graph \
 		repo/.git repo "$(git -C repo rev-parse one)" >actual &&
-	echo $(git -C repo rev-parse one^{tree}) >expect &&
+	git -C repo rev-parse one^{tree} >expect &&
 	test_cmp expect actual
 '