Removed DARTIUM codegen for IDLS (sdk/lib/dartium)

tools/dom/templates/html/impl/impl_DocumentType.darttemplate

Index: tools/dom/templates/html/impl/impl_DocumentType.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_DocumentType.darttemplate b/tools/dom/templates/html/impl/impl_DocumentType.darttemplate
index aad415854c807c21e956dc3d2ee9c65501982845..05179101a261400dea80128f8558ae40b14e95d8 100644
--- a/tools/dom/templates/html/impl/impl_DocumentType.darttemplate
+++ b/tools/dom/templates/html/impl/impl_DocumentType.darttemplate
@@ -7,10 +7,5 @@ part of $LIBRARYNAME;
 @DocsEditable()
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 $!MEMBERS
-$if DARTIUM
-  // Override this methods for Dartium _DocumentType can't be abstract.
-  Element get nextElementSibling => _blink.BlinkDocumentType.instance.nextElementSibling_Getter_(this);
-  Element get previousElementSibling => _blink.BlinkDocumentType.instance.previousElementSibling_Getter_(this);
-$endif
 }