Bug 1445117 - Remove duplicates from nsGkAtoms. r=froydnj

In each case, the atom had an obvious name and a weird name. Where possible, I
kept the obvious name and commented out the weird name, viz:

- `mixed` over `_mixed` for "mixed"
- `el` over `el_` for "el"
- `other` over `other_` for "other"
- `remote` over `Remote` for "remote"

But for several of them I didn't do that, because the weird name is used
within the HTML5 parser -- which is a huge pain to modify because it involves
code generated by code from another repo -- so I kept the weird name and
commented out the obvious name, viz:

- `list_` over `list` for "list"
- `svgSwitch` over `_switch` for "switch"
- `set_` over `set` for "set"

MozReview-Commit-ID: Jp3CpdWXNDm

dom/html/HTMLInputElement.cpp

@@ -1843,7 +1843,7 @@ nsGenericHTMLElement*
 HTMLInputElement::GetList() const
 {
   nsAutoString dataListId;
-  GetAttr(kNameSpaceID_None, nsGkAtoms::list, dataListId);
+  GetAttr(kNameSpaceID_None, nsGkAtoms::list_, dataListId);
   if (dataListId.IsEmpty()) {
     return nullptr;
   }