LibWeb/CSS: Remove PropertyID::Invalid

Author: https://github.com/AtkinsSJ
Commit: a098b5fcc4
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6347
Reviewed-by: https://github.com/gmta ✅

Tests/LibWeb/TestCSSInheritedProperty.cpp

@@ -22,7 +22,6 @@ TEST_CASE(is_inherited_property_test)
     EXPECT(!CSS::is_inherited_property(CSS::PropertyID::Border));
 
     // Edge cases
-    EXPECT(!CSS::is_inherited_property(CSS::PropertyID::Invalid));
     EXPECT(!CSS::is_inherited_property(CSS::PropertyID::All));
 }