download_toolchains no longer delete old toolchain directories.
download_toolchains no longer delete old toolchain directories.

It is no longer necessary to delete old toolchain directories using the
download_toolchains.py script. This section of the code also gave an
error if no toolchain directory existed.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3816
R=bradnelson@google.com

Review URL: https://codereview.chromium.org/253753008

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13091 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client