Intermediate step in removal of Base

We are marking types that will be Nexters and ResultNexters (I want a
better name for this one).

graph/iterator/fixed_iterator.go

@@ -57,13 +57,11 @@ func newFixed() *Fixed {
 
 // Creates a new Fixed iterator with a custom comparitor.
 func NewFixedIteratorWithCompare(compareFn Equality) *Fixed {
-	it := Fixed{
+	return &Fixed{
 		uid:    NextUID(),
 		values: make([]graph.Value, 0, 20),
 		cmp:    compareFn,
 	}
-	BaseInit(&it.Base)
-	return &it
 }
 
 func (it *Fixed) UID() uint64 {
@@ -159,6 +157,10 @@ func (it *Fixed) Result() graph.Value {
 	return it.result
 }
 
+func (it *Fixed) NextResult() bool {
+	return false
+}
+
 // No sub-iterators.
 func (it *Fixed) SubIterators() []graph.Iterator {
 	return nil