Remove usage of wslu

[anaisbetts]

This PR is simplified version of #198 - Windows 10 does not allow installing the OS to locations other than C:\Windows so fetching %systemroot% is unnecessary here (and since WSL is exclusive to Windows 10, we do not need to worry about Win7 here). WSL also handles marshaling paths between WSL and Windows, so we don't need to convert this path manually.

Fixes #198
Fixes #200
Fixes #204

[anaisbetts]

This line is for standard Win32, where we may be running under Win7 where installing to a different location may be possible - luckily we can just fetch %SYSTEMROOT% here

[sindresorhus]

Thanks :)

[jonaskuske]

Seeing this too late, but:

Windows 10 does not allow installing the OS to locations other than C:\Windows so fetching %systemroot% is unnecessary here

The Windows location is configurable (in WSL) – so while this PR hard-coded /mnt/c/, it could also be just /c/ or /windows/c/ or anything else! The wslpath utility from wslu (that was removed by this PR) handled this case, so did the previous PR (that was closed in favor of this PR). We'll need an alternative – I guess parsing /etc/wslconf in JS as suggested in the review here is still an option?

[anaisbetts]

Why would anyone do this other than a desire to have their tools be less reliable?

[jonaskuske]

@anaisbetts
When WSL was first introduced, mounting your drives directly into / was necessary if you wanted to run Docker, that's why it's still set up this way on some of my devices. Don't know if any (non-legacy) reasons to do so remain... But it's definitely still supported, even now with WSL2: https://docs.microsoft.com/en-US/windows/wsl/wsl-config#automount