unionfs: remove TestUnionFsFdLeak

TestUnionFsFdLeak looks at global state of the program, and is flaky:
the splice pool keeps open file descriptors, and its number depends on
how many read threads are scheduled in parallel.

unionfs/unionfs_linux_test.go

-// Copyright 2016 the Go-FUSE Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package unionfs
-
-import (
-	"io/ioutil"
-	"testing"
-)
-
-func TestUnionFsFdLeak(t *testing.T) {
-	beforeEntries, err := ioutil.ReadDir("/proc/self/fd")
-	if err != nil {
-		t.Fatalf("ReadDir failed: %v", err)
-	}
-
-	wd, clean := setupUfs(t)
-	err = ioutil.WriteFile(wd+"/ro/file", []byte("blablabla"), 0644)
-	if err != nil {
-		t.Fatalf("WriteFile failed: %v", err)
-	}
-	setRecursiveWritable(t, wd+"/ro", false)
-
-	contents, err := ioutil.ReadFile(wd + "/mnt/file")
-	if err != nil {
-		t.Fatalf("ReadFile failed: %v", err)
-	}
-
-	err = ioutil.WriteFile(wd+"/mnt/file", contents, 0644)
-	if err != nil {
-		t.Fatalf("WriteFile failed: %v", err)
-	}
-
-	clean()
-
-	afterEntries, err := ioutil.ReadDir("/proc/self/fd")
-	if err != nil {
-		t.Fatalf("ReadDir failed: %v", err)
-	}
-
-	if len(afterEntries) != len(beforeEntries) {
-		t.Errorf("/proc/self/fd changed size: after %v before %v", len(beforeEntries), len(afterEntries))
-	}
-}