Bug 1628715 - Part 6: Remove unused and redundant AppendElements overload. r=xpcom-reviewers,nika

The AppendElements overload accepting a mozilla::Array<Item, Length> is
redundant, since that is convertible to a mozilla::Span<const Item>, for which
a separate overload exists.

Differential Revision: https://phabricator.services.mozilla.com/D70386

xpcom/ds/nsTArray.h

@@ -1751,11 +1751,6 @@ class nsTArray_Impl
     return AppendElements<Item, ActualAlloc>(aSpan.Elements(), aSpan.Length());
   }
 
-  template <class Item, size_t Length, typename ActualAlloc = Alloc>
-  elem_type* AppendElements(const mozilla::Array<Item, Length>& aArray) {
-    return AppendElements<Item, ActualAlloc>(&aArray[0], Length);
-  }
-
  public:
   template <class Item>
   /* [[nodiscard]] */