Remove deprecated functions from comment for IPC::TestSink.
Remove deprecated functions from comment for IPC::TestSink.

Use RunLoop instead of MessageLoop.

BUG=none

Review URL: https://codereview.chromium.org/1801093002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#381531}

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