Remove WebElementLinkIsLiveKey

[Daniel Bates]

Following up on Darin Adler's remark in <https://bugs.webkit.org/show_bug.cgi?id=141597#c9>, we should look to remove WebElementLinkIsLiveKey and its related logic if it is not needed.

[Ahmad Saleem]

Still exist in WebKit Legacy realm.

https://searchfox.org/wubkat/rev/711120e7edec012527620d07bf63d85713a180fd/Source/WebKitLegacy/mac/Misc/WebElementDictionary.mm#103

https://searchfox.org/wubkat/rev/711120e7edec012527620d07bf63d85713a180fd/Source/WebKitLegacy/mac/WebKit.exp#196

https://searchfox.org/wubkat/rev/711120e7edec012527620d07bf63d85713a180fd/Source/WebKitLegacy/mac/WebView/WebView.mm#882

https://searchfox.org/wubkat/rev/711120e7edec012527620d07bf63d85713a180fd/Source/WebKitLegacy/mac/WebView/WebViewPrivate.h#84

@Alexey - are we planning to make changes around this in WebKit Legacy?

[Alexey Proskuryakov]

Removing unused SPI from WebKitLegacy would still be desirable, yes.