Remove unused BlankAnchorTargetImpliesNoOpenerEnabled

https://bugs.webkit.org/show_bug.cgi?id=247962
<rdar://problem/102390126>

Reviewed by Timothy Hatcher.

We added a feature flag years ago to enable us to A/B test this behavior and
debug site issues. In the years since, the spec and other browsers have aligned
on this behavior and we no longer need this flag.

* Source/WTF/Scripts/Preferences/WebPreferencesExperimental.yaml:
* Source/WebCore/html/HTMLAnchorElement.cpp:
(WebCore::HTMLAnchorElement::handleClick):
* Source/WebCore/html/HTMLFormElement.cpp:
(WebCore::HTMLFormElement::submit):

Canonical link: https://commits.webkit.org/257075@main

Source/WTF/Scripts/Preferences/WebPreferencesExperimental.yaml

@@ -142,18 +142,6 @@ AudioDescriptionsEnabled:
     WebCore:
       default: false
 
-BlankAnchorTargetImpliesNoOpenerEnabled:
-  type: bool
-  humanReadableName: "Blank anchor target implies rel=noopener"
-  humanReadableDescription: "target=_blank on anchor elements implies rel=noopener"
-  defaultValue:
-    WebKitLegacy:
-      default: true
-    WebKit:
-      default: true
-    WebCore:
-      default: true
-
 # We would have to partition BroadcastChannel based on PageGroups if we wanted to enable this for WebKitLegacy.
 BroadcastChannelEnabled:
   type: bool

Source/WebCore/html/HTMLAnchorElement.cpp

@@ -604,7 +604,7 @@ void HTMLAnchorElement::handleClick(Event& event)
 
     auto effectiveTarget = this->effectiveTarget();
     NewFrameOpenerPolicy newFrameOpenerPolicy = NewFrameOpenerPolicy::Allow;
-    if (hasRel(Relation::NoOpener) || hasRel(Relation::NoReferrer) || (!hasRel(Relation::Opener) && document().settings().blankAnchorTargetImpliesNoOpenerEnabled() && isBlankTargetFrameName(effectiveTarget) && !completedURL.protocolIsJavaScript()))
+    if (hasRel(Relation::NoOpener) || hasRel(Relation::NoReferrer) || (!hasRel(Relation::Opener) && isBlankTargetFrameName(effectiveTarget) && !completedURL.protocolIsJavaScript()))
         newFrameOpenerPolicy = NewFrameOpenerPolicy::Suppress;
 
     auto privateClickMeasurement = parsePrivateClickMeasurement(completedURL);

Source/WebCore/html/HTMLFormElement.cpp

@@ -444,7 +444,7 @@ void HTMLFormElement::submit(Event* event, bool processingUserGesture, FormSubmi
         return;
 
     auto relAttributes = parseFormRelAttributes(getAttribute(HTMLNames::relAttr));
-    if (relAttributes.noopener || relAttributes.noreferrer || (!relAttributes.opener && document().settings().blankAnchorTargetImpliesNoOpenerEnabled() && isBlankTargetFrameName(formSubmission->target()) && !formSubmission->requestURL().protocolIsJavaScript()))
+    if (relAttributes.noopener || relAttributes.noreferrer || (!relAttributes.opener && isBlankTargetFrameName(formSubmission->target()) && !formSubmission->requestURL().protocolIsJavaScript()))
         formSubmission->setNewFrameOpenerPolicy(NewFrameOpenerPolicy::Suppress);
     if (relAttributes.noreferrer)
         formSubmission->setReferrerPolicy(ReferrerPolicy::NoReferrer);