[Telemetry] Remove a 2.7 polyfill now that we depend on 2.7.
[Telemetry] Remove a 2.7 polyfill now that we depend on 2.7.

BUG=

Review URL: https://codereview.chromium.org/155483002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@249487 0039d316-1c4b-4281-b951-d872f2087c98

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