golangci-lint: fix issues found by "unused" and "deadcode"

Except xattrSupported, this is a false positive.

$ golangci-lint run --disable-all --enable unused --enable deadcode
gocryptfs-xray/xray_main.go:24:5: `GitVersionFuse` is unused (deadcode)
var GitVersionFuse = "[GitVersionFuse not set - please compile using ./build.bash]"
    ^
tests/symlink_race/main.go:47:6: `chmodLoop` is unused (deadcode)
func chmodLoop() {
     ^
internal/readpassword/extpass_test.go:11:5: `testPw` is unused (deadcode)
var testPw = []byte("test")
    ^
tests/reverse/xattr_test.go:13:6: func `xattrSupported` is unused (unused)
func xattrSupported(path string) bool {
     ^
internal/fusefrontend_reverse/rpath.go:20:22: func `(*RootNode).abs` is unused (unused)
func (rfs *RootNode) abs(relPath string, err error) (string, error) {
                     ^
tests/matrix/matrix_test.go:310:6: `sContains` is unused (deadcode)
func sContains(haystack []string, needle string) bool {

1 files changed, 0 insertions, 14 deletions

diff --git a/tests/symlink_race/main.go b/tests/symlink_race/main.go
index 6fb794f..8474a83 100644
--- a/tests/symlink_race/main.go
+++ b/tests/symlink_race/main.go
@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"os"
 	"syscall"
-	"time"
 )
 
 const (
@@ -44,19 +43,6 @@ func renameLoop() {
 	}
 }
 
-func chmodLoop() {
-	var err error
-	for {
-		err = syscall.Chmod(testFile, 0777)
-		if err != nil {
-			fmt.Printf("Chmod() failed: %v\n", err)
-		} else {
-			fmt.Printf("Chmod() ok\n")
-		}
-		time.Sleep(100 * time.Microsecond)
-	}
-}
-
 func openLoop() {
 	var err error
 	var f *os.File