LibWeb: Remove `m_src_is_set` field from `HTMLScriptElement`

Now that we pass an `old_value` parameter to `attribute_changed` it is
no longer necessary to store the current attribute state in
`HTMLScriptElement`.

Userland/Libraries/LibWeb/HTML/HTMLScriptElement.cpp

@@ -59,13 +59,11 @@ void HTMLScriptElement::attribute_changed(FlyString const& name, Optional<String
     } else if (name == HTML::AttributeNames::referrerpolicy) {
         m_referrer_policy = ReferrerPolicy::from_string(value.value_or(""_string)).value_or(ReferrerPolicy::ReferrerPolicy::EmptyString);
     } else if (name == HTML::AttributeNames::src) {
-        bool old_src_is_set = m_src_is_set;
-        m_src_is_set = value.has_value();
         // https://html.spec.whatwg.org/multipage/scripting.html#script-processing-model
         // When a script element el that is not parser-inserted experiences one of the events listed in the following list, the user agent must immediately prepare the script element el:
         // - [...]
         // - The script element is connected and has a src attribute set where previously the element had no such attribute.
-        if (!is_parser_inserted() && is_connected() && !old_src_is_set && m_src_is_set) {
+        if (!is_parser_inserted() && is_connected() && value.has_value() && !old_value.has_value()) {
             prepare_script();
         }
     }

Userland/Libraries/LibWeb/HTML/HTMLScriptElement.h

@@ -135,8 +135,6 @@ private:
     Optional<DOM::DocumentLoadEventDelayer> m_document_load_event_delayer;
 
     size_t m_source_line_number { 1 };
-
-    bool m_src_is_set = false;
 };
 
 }