Remove unused UseCounter features
Remove unused UseCounter features

These are the reviews in which the enum values became unused:

AnimationConstructorKeyframeListEffectDoubleTiming and
ElementAnimateKeyframeListEffect*Timing:
https://codereview.chromium.org/947923002

AudioContextCreateStereoPanner (never used):
https://codereview.chromium.org/799403007

DevToolsConsoleTimeline:
https://codereview.chromium.org/750983003

DOMImplementationHasFeature*:
https://codereview.chromium.org/1108293002

FontFaceSetReady:
https://codereview.chromium.org/816923002

MixedContentPrivateIPInPublicWebsiteActive/Passive:
https://codereview.chromium.org/842783002

ServiceWorkerClientsGetAll:
https://codereview.chromium.org/1056973003

TimelineStart:
https://codereview.chromium.org/1113173003

Review URL: https://codereview.chromium.org/1141733002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@195305 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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