[sanitizer] Remove "null" for 256 allocations in test

Very rarely this case can return all non-null
for all allocations, making this test flaky.

Author: vitalybuka

compiler-rt/test/sanitizer_common/TestCases/Linux/soft_rss_limit_mb_test.cpp

@@ -63,7 +63,6 @@ int main() {
 // CHECK_MAY_RETURN_1: allocating 32 times
 // CHECK_MAY_RETURN_1: Some of the malloc calls returned non-null:
 // CHECK_MAY_RETURN_1: allocating 256 times
-// CHECK_MAY_RETURN_1: Some of the malloc calls returned null:
 // CHECK_MAY_RETURN_1: Some of the malloc calls returned non-null:
 // CHECK_MAY_RETURN_1: allocating 512 times
 // CHECK_MAY_RETURN_1: Some of the malloc calls returned null: