main: drop hardcoded /usr/bin/logger path

The hardcoded full paths were introduced to handle the
case of an empty PATH environment variable. However,
since commit 10212d791a we set PATH to a default
value if empty. The hardcoded paths are no longer neccessary,
and cause problems on some distros:

User voobscout on
https://github.com/rfjakob/gocryptfs/issues/225#issuecomment-438682034 :

  just to chime in - please don't hardcode paths, for example I'm on
  NixOS and logger lives in /run/current-system/sw/bin/logger

Drop the hardcoded paths.

daemonize.go

@@ -72,15 +72,9 @@ func redirectStdFds() {
 		return
 	}
 	tag := fmt.Sprintf("gocryptfs-%d-logger", os.Getpid())
-	// SUSE has /bin/logger, everybody else has /usr/bin/logger.
-	for _, path := range []string{"/usr/bin/logger", "/bin/logger"} {
-		cmd := exec.Command(path, "-t", tag)
+	cmd := exec.Command("logger", "-t", tag)
 	cmd.Stdin = pr
 	err = cmd.Start()
-		if err == nil {
-			break
-		}
-	}
 	if err != nil {
 		tlog.Warn.Printf("redirectStdFds: could not start logger: %v\n", err)
 		return