[WINLOGON] Clean up part 2

[WINLOGON] Clean up part 2
- Replace the UNICODE_STRING usMessage by a PWSTR pszMessage.
- Use the "%02d:%02d:%02d" time format and get rid of the safe string printf because the string will NEVER be longer than 8 characters.
- Rename the timer id constant because it is NOT a resource id.
- Rename variables according to the coding style.