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, 10 deletions

diff --git a/tests/matrix/matrix_test.go b/tests/matrix/matrix_test.go
index 5906b3c..5cc5251 100644
--- a/tests/matrix/matrix_test.go
+++ b/tests/matrix/matrix_test.go
@@ -306,16 +306,6 @@ func TestFileHoles(t *testing.T) {
 	}
 }
 
-// sContains - does the slice of strings "haystack" contain "needle"?
-func sContains(haystack []string, needle string) bool {
-	for _, element := range haystack {
-		if element == needle {
-			return true
-		}
-	}
-	return false
-}
-
 func TestRmwRace(t *testing.T) {
 
 	runtime.GOMAXPROCS(10)