LibWeb: Remove underlying realm from SyntheticRealmSettings

This was removed from the ShadowRealm HTML spec integration PR after my
suggestion as it is not used anywhere, and I don't believe it would ever
need to be used in the future or by other specs.

Libraries/LibWeb/HTML/Scripting/SyntheticRealmSettings.cpp

@@ -13,7 +13,6 @@ void SyntheticRealmSettings::visit_edges(JS::Cell::Visitor& visitor)
 {
     execution_context->visit_edges(visitor);
     visitor.visit(principal_realm);
-    visitor.visit(underlying_realm);
     visitor.visit(module_map);
 }
 

Libraries/LibWeb/HTML/Scripting/SyntheticRealmSettings.h

@@ -23,10 +23,6 @@ struct SyntheticRealmSettings {
     // The principal realm which this synthetic realm exists within.
     GC::Ref<JS::Realm> principal_realm;
 
-    // An underlying realm
-    // The synthetic realm which this settings object represents.
-    GC::Ref<JS::Realm> underlying_realm;
-
     // A module map
     // A module map that is used when importing JavaScript modules.
     GC::Ref<ModuleMap> module_map;