Revert "add cold.Index"

This reverts commit 5f06c00.

segment/cold/index.go

@@ -15,20 +15,12 @@ var skipFields = map[string]struct{}{
 	camel.Case(v1.Filters_Duration.String()): {},
 }
 
-type Index struct {
-	segment.Segment
-	DiskSize uint64
-}
-
-func New(r arrow.Record) (*Index, error) {
+func New(r arrow.Record) (segment.Segment, error) {
 	document := NewRecord(r, func(r arrow.Record, i int) bool {
 		_, ok := skipFields[r.ColumnName(i)]
 		return !ok
 	})
 	defer document.Release()
-	seg, size, err := ice.New([]segment.Document{document}, func(s string, i int) float32 { return 0 })
-	if err != nil {
-		return nil, err
-	}
-	return &Index{Segment: seg, DiskSize: size}, nil
+	seg, _, err := ice.New([]segment.Document{document}, func(s string, i int) float32 { return 0 })
+	return seg, err
 }