remove RealPathLister interface

This is a backward incompatible change but the RealPathLister was useless:
even if you implement this interface you can customize the response for
SSH_FXP_REALPATH packets, but response for other packets still convert paths
using "/" as base

request-example.go

@@ -464,19 +464,10 @@ func (fs *root) Lstat(r *Request) (ListerAt, error) {
 	return listerat{file}, nil
 }
 
-// implements RealpathFileLister interface
-func (fs *root) Realpath(p string) string {
-	if fs.startDirectory == "" || fs.startDirectory == "/" {
-		return cleanPath(p)
-	}
-	return cleanPathWithBase(fs.startDirectory, p)
-}
-
 // In memory file-system-y thing that the Hanlders live on
 type root struct {
-	rootFile       *memFile
-	mockErr        error
-	startDirectory string
+	rootFile *memFile
+	mockErr  error
 
 	mu    sync.Mutex
 	files map[string]*memFile

request-interfaces.go

@@ -86,15 +86,6 @@ type LstatFileLister interface {
 	Lstat(*Request) (ListerAt, error)
 }
 
-// RealPathFileLister is a FileLister that implements the Realpath method.
-// We use "/" as start directory for relative paths, implementing this
-// interface you can customize the start directory.
-// You have to return an absolute POSIX path.
-type RealPathFileLister interface {
-	FileLister
-	RealPath(string) string
-}
-
 // NameLookupFileLister is a FileLister that implmeents the LookupUsername and LookupGroupName methods.
 // If this interface is implemented, then longname ls formatting will use these to convert usernames and groupnames.
 type NameLookupFileLister interface {

request-server.go

@@ -218,13 +218,7 @@ func (rs *RequestServer) packetWorker(ctx context.Context, pktChan chan orderedR
 			handle := pkt.getHandle()
 			rpkt = statusFromError(pkt.ID, rs.closeRequest(handle))
 		case *sshFxpRealpathPacket:
-			var realPath string
-			if realPather, ok := rs.Handlers.FileList.(RealPathFileLister); ok {
-				realPath = realPather.RealPath(pkt.getPath())
-			} else {
-				realPath = cleanPathWithBase(rs.startDirectory, pkt.getPath())
-			}
-			rpkt = cleanPacketPath(pkt, realPath)
+			rpkt = cleanPacketPath(pkt, cleanPathWithBase(rs.startDirectory, pkt.getPath()))
 		case *sshFxpOpendirPacket:
 			request := requestFromPacket(ctx, pkt, rs.startDirectory)
 			handle := rs.nextRequest(request)

request-server_test.go

@@ -7,7 +7,6 @@ import (
 	"io/ioutil"
 	"net"
 	"os"
-	"path"
 	"runtime"
 	"testing"
 	"time"
@@ -809,25 +808,6 @@ func TestUncleanDisconnect(t *testing.T) {
 	checkRequestServerAllocator(t, p)
 }
 
-func TestRealPath(t *testing.T) {
-	root := &root{
-		rootFile:       &memFile{name: "/", modtime: time.Now(), isdir: true},
-		files:          make(map[string]*memFile),
-		startDirectory: "/apath",
-	}
-
-	p := root.Realpath(".")
-	assert.Equal(t, root.startDirectory, p)
-	p = root.Realpath("/")
-	assert.Equal(t, "/", p)
-	p = root.Realpath("..")
-	assert.Equal(t, "/", p)
-	p = root.Realpath("../../..")
-	assert.Equal(t, "/", p)
-	p = root.Realpath("relpath")
-	assert.Equal(t, path.Join(root.startDirectory, "relpath"), p)
-}
-
 func TestCleanPath(t *testing.T) {
 	assert.Equal(t, "/", cleanPath("/"))
 	assert.Equal(t, "/", cleanPath("."))