Remove code for losing activation when child window activated.
Remove code for losing activation when child window activated.

This was intended only for use with NPAPI (now dead), and causes issues by thinking it can activate the DirectComposition child window.

BUG=580938

Review URL: https://codereview.chromium.org/1630873003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#371960}

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