t5801 (remote-helpers): cleanup environment sets

Commit 512477b (tests: use "env" to run commands with temporary env-var
settings) missed some variables in the remote-helpers test. Also
standardize these.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5801-remote-helpers.sh

@@ -212,9 +212,8 @@ test_expect_success 'push update refs failure' '
 	echo "update fail" >>file &&
 	git commit -a -m "update fail" &&
 	git rev-parse --verify testgit/origin/heads/update >expect &&
-	GIT_REMOTE_TESTGIT_PUSH_ERROR="non-fast forward" &&
-	export GIT_REMOTE_TESTGIT_PUSH_ERROR &&
-	test_expect_code 1 git push origin update &&
+	test_expect_code 1 env GIT_REMOTE_TESTGIT_FAILURE="non-fast forward" \
+		git push origin update &&
 	git rev-parse --verify testgit/origin/heads/update >actual &&
 	test_cmp expect actual
 	)
@@ -235,10 +234,8 @@ cmp_marks () {
 }
 
 test_expect_success 'proper failure checks for fetching' '
-	(GIT_REMOTE_TESTGIT_FAILURE=1 &&
-	export GIT_REMOTE_TESTGIT_FAILURE &&
-	cd local &&
-	test_must_fail git fetch 2> error &&
+	(cd local &&
+	test_must_fail env GIT_REMOTE_TESTGIT_FAILURE=1 git fetch 2>error &&
 	cat error &&
 	grep -q "Error while running fast-import" error
 	)