Remove node count checks from fast/dom/gc-dom-tree-lifetime.html

Before this CL, the test result depended on synchronous gc() call
which was non-determistic after Oilpan.
This CL removes the node count check to make the test runs deterministic.

This change is safe, as the leak checks are now ensured by Blink Leak Detector,
which supports Oilpan.

BUG=606649

Review-Url: https://codereview.chromium.org/2025773002
Cr-Commit-Position: refs/heads/master@{#396774}
2 files changed