A exclusão de duplicatas na variável de ambiente Path não alterará nada. No entanto,
The %SystemRoot% variable is a special system-wide environment variable found on Microsoft Windows NT and its derivatives. Its value is the location of the system directory, including the drive and path. The drive is the same as %SystemDrive% and the default path on a clean installation depends upon the version of the operating system. By default, Windows NT 5.1 (Windows XP) and newer versions use \WINDOWS, Windows NT 5.0 (Windows 2000), Windows NT 4.0 and Windows NT 3.1 use \WINNT, Windows NT 3.5x uses \WINNT35, and Windows NT 4.0 Terminal Server uses \WTSRV
Deve ser seguro remover as duplicatas [% systemroot%, C: \ windows] se você estiver usando o Windows XP ou mais recente.