Update BindTest.ScopedRefptr expectation and its comment
Update BindTest.ScopedRefptr expectation and its comment

The bug described in the removed comment is already fixed in
crbug.com/589048.

BUG=251937,589048

Review-Url: https://codereview.chromium.org/1966143002
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#393177}

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