Issue #3049 - Undo Stylo nonsense that breaks body and frame margins.

This restores support for using HTML tag styling of margins on the body.
Reftests post bug still pass for dynamic changes, so does the newly-added
test for body margins and frames that tests the old styling method.
This also removes the reftest list for stylo testing for obvious reasons.

dom/html/HTMLTableCellElement.cpp

@@ -106,7 +106,9 @@ HTMLTableCellElement::WalkContentStyleRules(nsRuleWalker* aRuleWalker)
   nsresult rv = nsGenericHTMLElement::WalkContentStyleRules(aRuleWalker);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  if (nsMappedAttributes* tableInheritedAttributes = GetMappedAttributesInheritedFromTable()) {
+  if (HTMLTableElement* table = GetTable()) {
+    nsMappedAttributes* tableInheritedAttributes =
+      table->GetAttributesMappedForCell();
     if (tableInheritedAttributes) {
       aRuleWalker->Forward(tableInheritedAttributes);
     }
@@ -114,16 +116,6 @@ HTMLTableCellElement::WalkContentStyleRules(nsRuleWalker* aRuleWalker)
   return NS_OK;
 }
 
-nsMappedAttributes*
-HTMLTableCellElement::GetMappedAttributesInheritedFromTable() const
-{
-  if (HTMLTableElement* table = GetTable()) {
-    return table->GetAttributesMappedForCell();
-  }
-
-  return nullptr;
-}
-
 NS_IMETHODIMP
 HTMLTableCellElement::SetAbbr(const nsAString& aAbbr)
 {