Return value {#FSNAME} on windows should not be backslashed

Returned values for

in vfs.fs.discovery should return just the drive letter and ":" (eg. C
Right now, it returns the drive letter, ":" and a backlash (eg. C:) which cannot be used in performance counters which take the drive letter without backslash.

I think it's a change small enough to not break compatibility with existing templates.