Fix heap size tracing during bulk thread-local allocations.

The value passed to Heap::TraceHeapSize in
Heap::AllocObjectWithAllocator during bulk TL allocation was
incorrectly taking into account `bytes_tl_bulk_allocated` twice.

Test: m test-art-host
Change-Id: If0219d8da08d8a1e84969d8e5426ade646b24dd7