pkg/system: windows: setCTime(): remove redundant conversion
pkg/system: windows: setCTime(): remove redundant conversion

It looks like this function was converting the time (`windows.NsecToTimespec()`),
only to convert it back (`windows.TimespecToNsec()`). This became clear when
moving the lines together:

```go
ctimespec := windows.NsecToTimespec(ctime.UnixNano())
c := windows.NsecToFiletime(windows.TimespecToNsec(ctimespec))
```

And looking at the Golang code, it looks like they're indeed the exact reverse:

```go
func TimespecToNsec(ts Timespec) int64 { return int64(ts.Sec)*1e9 + int64(ts.Nsec) }

func NsecToTimespec(nsec int64) (ts Timespec) {
    ts.Sec = nsec / 1e9
    ts.Nsec = nsec % 1e9
    return
}
```

While modifying this code, also renaming the `e` variable to a more common `err`.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

thaJeztah/docker,jimjag/docker,konstruktoid/docker-upstream,mahak/docker,trebonian/docker,Mokolea/docker,Mokolea/docker,jimjag/docker,mahak/docker,trebonian/docker,jimjag/docker,Mokolea/docker,konstruktoid/docker-upstream,trebonian/docker,thaJeztah/docker,jimjag/docker,konstruktoid/docker-upstream,mahak/docker,moby/moby,Ramzec/docker,moby/moby,moby/moby,Ramzec/docker,Mokolea/docker,trebonian/docker,moby/moby,konstruktoid/docker-upstream,thaJeztah/docker,Ramzec/docker,mahak/docker,thaJeztah/docker,Ramzec/docker