[hivesys] Change Temp directory

In "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment', change the values of both TEMP and TMP from "%SystemDrive%\TEMP" into "%SystemRoot%\Temp". This removes the UNIX-like folder C:\TEMP that is created on ReactOS when syssetup is running, and instead uses "C:\ReactOS\Temp". These are also the values used in XP/2003.