remove closer type assertions

We no longer need them.

basic_ds.go

 package datastore
 
 import (
-	"io"
 	"log"
 
 	dsq "github.com/ipfs/go-datastore/query"
@@ -244,10 +243,7 @@ func (d *LogBatch) Commit() (err error) {
 
 func (d *LogDatastore) Close() error {
 	log.Printf("%s: Close\n", d.Name)
-	if cds, ok := d.child.(io.Closer); ok {
-		return cds.Close()
-	}
-	return nil
+	return d.child.Close()
 }
 
 func (d *LogDatastore) Check() error {

keytransform/keytransform.go

 package keytransform
 
 import (
-	"io"
-
 	ds "github.com/ipfs/go-datastore"
 	dsq "github.com/ipfs/go-datastore/query"
 )
@@ -84,10 +82,7 @@ func (d *ktds) Query(q dsq.Query) (dsq.Results, error) {
 }
 
 func (d *ktds) Close() error {
-	if c, ok := d.child.(io.Closer); ok {
-		return c.Close()
-	}
-	return nil
+	return d.child.Close()
 }
 
 // DiskUsage implements the PersistentDatastore interface.

mount/mount.go

@@ -5,7 +5,6 @@ package mount
 import (
 	"errors"
 	"fmt"
-	"io"
 	"sort"
 	"strings"
 	"sync"
@@ -195,11 +194,9 @@ func (d *Datastore) IsThreadSafe() {}
 
 func (d *Datastore) Close() error {
 	for _, d := range d.mounts {
-		if c, ok := d.Datastore.(io.Closer); ok {
-			err := c.Close()
-			if err != nil {
-				return err
-			}
+		err := d.Datastore.Close()
+		if err != nil {
+			return err
 		}
 	}
 	return nil

sync/sync.go

 package sync
 
 import (
-	"io"
 	"sync"
 
 	ds "github.com/ipfs/go-datastore"
@@ -93,10 +92,7 @@ func (d *MutexDatastore) Batch() (ds.Batch, error) {
 func (d *MutexDatastore) Close() error {
 	d.RWMutex.Lock()
 	defer d.RWMutex.Unlock()
-	if c, ok := d.child.(io.Closer); ok {
-		return c.Close()
-	}
-	return nil
+	return d.child.Close()
 }
 
 // DiskUsage implements the PersistentDatastore interface.