The get-toolchain script still contained leftover goop for installing
the UCRT, even though that misguided plan was abandoned last year. This
change deletes that.

The get-toolchain script also confusingly used the vs2013_files
directory for anything that wasn't VS 2015. It doesn't technically make
any difference now that we use hashes for the toolchain directories, but
it was confusing when experimenting with VS 2017.

R=sebmarchand@chromium.org
BUG=683729

Change-Id: Ie0d3eccffe4796d4c5e23a28276acdd757e290d4
Reviewed-on: https://chromium-review.googlesource.com/453122Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>