Delete now unused StyleDifferenceContextSensitiveProperty enum
Delete now unused StyleDifferenceContextSensitiveProperty enum

After https://src.chromium.org/viewvc/blink?view=rev&revision=177358
these enumeration values are unused.

Review URL: https://codereview.chromium.org/366813004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@177391 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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