LibWeb: Remove DOM element deprecated_get_attribute()

Author: https://github.com/bplaat
Commit: a681429dff
Pull-request: https://github.com/SerenityOS/serenity/pull/22777
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/shannonbooth ✅

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -369,7 +369,7 @@ String HTMLInputElement::value() const
         || type_state() == TypeAttributeState::ResetButton
         || type_state() == TypeAttributeState::Button) {
         // On getting, if the element has a value content attribute, return that attribute's value; otherwise, return the empty string.
-        return get_attribute(AttributeNames::value).value_or(String {});
+        return get_attribute_value(AttributeNames::value);
     }
 
     // https://html.spec.whatwg.org/multipage/input.html#range-state-(type=range):attr-input-value
@@ -1015,7 +1015,7 @@ void HTMLInputElement::reset_algorithm()
     m_dirty_checkedness = false;
 
     // set the value of the element to the value of the value content attribute, if there is one, or the empty string otherwise,
-    m_value = get_attribute(AttributeNames::value).value_or(String {});
+    m_value = get_attribute_value(AttributeNames::value);
 
     // set the checkedness of the element to true if the element has a checked content attribute and false if it does not,
     m_checked = has_attribute(AttributeNames::checked);