[std] Don't sync toolchain() and tools() as tarballs anymore

[kylewlacy]

Blocked until Brioche >v0.1.4

In #147, the std.toolchain() and std.tools() recipes were tweaked to wrap the results in a tarball, which helped speed up downloads when using Brioche v0.1.4 due to both artifacts having lots of blobs.

brioche-dev/brioche#179 has been merged into the main branch of Brioche and is queued to go out in the next release. The new cache greatly speeds up syncing when downloading artifacts with lots of blobs. Explicitly wrapping std.toolchain() and std.tools() will no longer help performance, but using a compressed tarball will lead to more storage used in the cache (due to how artifacts are broken up using a content-defined chunking algorithm). So, we should revert #147 once the next version of Brioche is released supporting the new cache.