media: Disable the unified media pipeline for API levels 16 & 17
media: Disable the unified media pipeline for API levels 16 & 17

AVDA still has bugs on these older platform versions so this CL disables
the unified media pipeline trial on them.

BUG=597467

Review URL: https://codereview.chromium.org/1825913003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#383608}

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