Remove an outdated/inapplicable comment
Remove an outdated/inapplicable comment

Summary: [Folly] Remove an outdated/inapplicable comment from `folly/Portability.h`.

Reviewed By: Gownta

Differential Revision: D3055909

fb-gh-sync-id: c17fdcc7de13fe5a9bb38bb4498a006ec71a61e2
shipit-source-id: c17fdcc7de13fe5a9bb38bb4498a006ec71a61e2

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