os: remove unused testingForceReadDirLstat

It was introduced in CL 261540 but never set by any test.

Change-Id: Id2a59c58ed510b6041cc51ce47ab79199a60b215
Reviewed-on: https://go-review.googlesource.com/c/go/+/655797
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>

src/os/dir.go

@@ -106,10 +106,6 @@ func (f *File) ReadDir(n int) ([]DirEntry, error) {
 	return dirents, err
 }
 
-// testingForceReadDirLstat forces ReadDir to call Lstat, for testing that code path.
-// This can be difficult to provoke on some Unix systems otherwise.
-var testingForceReadDirLstat bool
-
 // ReadDir reads the named directory,
 // returning all its directory entries sorted by filename.
 // If an error occurs reading the directory,

src/os/export_test.go

@@ -9,7 +9,6 @@ package os
 var Atime = atime
 var LstatP = &lstat
 var ErrWriteAtInAppendMode = errWriteAtInAppendMode
-var TestingForceReadDirLstat = &testingForceReadDirLstat
 var ErrPatternHasSeparator = errPatternHasSeparator
 
 func init() {

src/os/file_unix.go

@@ -482,7 +482,7 @@ func newUnixDirent(parent, name string, typ FileMode) (DirEntry, error) {
 		name:   name,
 		typ:    typ,
 	}
-	if typ != ^FileMode(0) && !testingForceReadDirLstat {
+	if typ != ^FileMode(0) {
 		return ude, nil
 	}