scoped_ptr<> is now an alias of std::unique_ptr<> on Linux. So on Linux,
the test is no longer needed in Chromium. Since no one seems to care the
test on the other OSes than Linux, it's time to drop it.

BUG=554298

Review URL: https://codereview.chromium.org/1765833002

Cr-Commit-Position: refs/heads/master@{#379454}