Simplify the QUIC host whitelist since embedders can the whitelist extension.
Simplify the QUIC host whitelist since embedders can the whitelist extension.

BUG=576402

Review URL: https://codereview.chromium.org/1590533004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#369957}

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