Docs: Remove `minimal-ui` related information

From https://developer.apple.com/library/prerelease/ios/releasenotes/General/RN-iOSSDK-8.0/#//apple_ref/doc/uid/TP40014223-CH1-SW83: 

>  The minimal-ui viewport property is no longer supported in iOS 8.

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The [`minimal-ui`](https://github.com/h5bp/html5-boilerplate/commit/f4a2cbfcadff23ec02cb6afdf7a95bf0ad602dd1) viewport property was introduced in iOS 7.1, and it seems that it will no longer be supported in iOS 8, so I think we shouldn't encourage its usage anymore.