t: remove TEST_PASSES_SANITIZE_LEAK annotations

Now that the default value for TEST_PASSES_SANITIZE_LEAK is `true` there
is no longer a need to have that variable declared in all of our tests.
Drop it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t2002-checkout-cache-u.sh

@@ -8,7 +8,6 @@ test_description='git checkout-index -u test.
 With -u flag, git checkout-index internally runs the equivalent of
 git update-index --refresh on the checked out entry.'
 
-TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success \