fix staticcheck

This commit was moved from ipfs/go-ipfs-files@5dc5da5

files/multifilereader_test.go

@@ -30,11 +30,7 @@ func TestMultiFileReaderToMultiFile(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	md, ok := mf.(Directory)
-	if !ok {
-		t.Fatal("Expected a directory")
-	}
-	it := md.Entries()
+	it := mf.Entries()
 
 	if !it.Next() || it.Name() != "beep.txt" {
 		t.Fatal("iterator didn't work as expected")
@@ -80,11 +76,7 @@ func TestMultiFileReaderToMultiFileSkip(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	md, ok := mf.(Directory)
-	if !ok {
-		t.Fatal("Expected a directory")
-	}
-	it := md.Entries()
+	it := mf.Entries()
 
 	if !it.Next() || it.Name() != "beep.txt" {
 		t.Fatal("iterator didn't work as expected")