[0ssw9k] deprecate the rule "Scrollable content can be reached with sequential focus navigation"

[shunguoy]

With the recent update from Chrome, all major browsers (Chrome, Edge, FF) now support automatic focus on scrollable elements.
In Safari, the properties of being focusable and scrollable are independent of each other. A scrollable element can be scrolled without explicit focus. You can verify the behavior using the Failed Example 2. First, to make sure the focus is on the viewport (rather than in Tool Bar, etc.), then press down or up Arrow key (you may need multiple times) to observe the scrollbar is moving. You can further add a tabindex='-1' to verify the behavior.