since nobody knows about =dispose, rename the existing proc to deallocRef which is a much better name anyway

tests/destructor/tbintree2.nim

@@ -57,7 +57,7 @@ proc `=destroy`(t: var Tree) {.nodestroy.} =
     let x = s.pop
     if x.left != nil: s.add(x.left)
     if x.right != nil: s.add(x.right)
-    `=disposeHidden`(x)
+    deallocRef(x)
   `=destroy`(s)
 
 proc hasValue(self: var Tree, x: int32): bool =