Do not set HOME in julia .bat script

@vtjnash Are you ok with this? I noticed this while trying to get IJulia to run which uses HOME to locate some of its config files. The original reason we had this was because git needed, but we do that via `setenv` no anyway, so I don't see a reason to keep it. Thoughts?

The only thing that this would imply is that we'd have to tell users to use ```Git.git(`config user.name`)``` etc. instead of running git directly.