AX: Remove CSSDisplayContentsAXSupportEnabled flag

AX: Remove CSSDisplayContentsAXSupportEnabled flag
https://bugs.webkit.org/show_bug.cgi?id=240409

Reviewed by Chris Fleizach.

Source/WebCore:

We added initial support without using this flag and will continue to
fix bugs as we find them, making this flag unnecessary.

* page/RuntimeEnabledFeatures.h:
(WebCore::RuntimeEnabledFeatures::setCSSDisplayContentsAXSupportEnabled): Deleted.
(WebCore::RuntimeEnabledFeatures::cssDisplayContentsAXSupportEnabled const): Deleted.

Source/WebKitLegacy/mac:

We added initial support without using this flag and will continue to
fix bugs as we find them, making this flag unnecessary.

* WebView/WebPreferenceKeysPrivate.h:
* WebView/WebPreferences.mm:
(-[WebPreferences cssDisplayContentsAXSupportEnabled]): Deleted.
(-[WebPreferences setCSSDisplayContentsAXSupportEnabled:]): Deleted.
* WebView/WebPreferencesPrivate.h:

Source/WTF:

* Scripts/Preferences/WebPreferencesInternal.yaml:

Tools:

* DumpRenderTree/TestOptions.cpp:
(WTR::TestOptions::defaults):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@294208 268f45cc-cd09-0410-ab3c-d52691b4dbfc