infra: Remove named vs_toolchain cache. This is no longer needed now that ANGLE uses the pinned depot_tools. We should land this after the recipe updates to no longer use the cache. Patch series: 1. http://crrev.com/c/2819943 2. http://crrev.com/c/2819472 3. This CL Bug: angleproject:5842 Change-Id: I5d166c7cd66a9d7f077c09b4149de08b22724af8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2819945 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>