fix #252 and #302 after vscode update to 1.5.1

Remote debugging broke again after VSCode updated to 1.5.1.

Reading your first fix to #252, I understood that part of code better, I think. And I still believe that using platform specific version of path to tackle with remote paths should solve the problems, e.g. path.sep, path.resolve, etc. Ref: https://nodejs.org/api/path.html#path_windows_vs_posix

So I changed the logic a bit, but couldn't come up with a better name than path2, to avoid name conflict with remotePath, name of the argument.

I also removed the call to validatePathSync(), not seeing its effect, since I believed once path were platform specific, there should be no problems.

Correct me if I'm wrong. Thanks!