Don't delete toolchain on each build.
Don't delete toolchain on each build.

The valgrind bots are clobbering the toolchain on each build.
Let's instead rely on the downloader script to keep things up to date.

R=nfullagar@google.com
BUG=None
TEST=None

Review URL: https://chromiumcodereview.appspot.com/10808033

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@9183 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client