sweet: remove sweet get -auth flag from README
sweet: remove sweet get -auth flag from README

Authentication is not required to download assets.

Change-Id: Ia2ba4a2acd57c40254026974b2c6eac35a5e0e61
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/449176
Auto-Submit: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Michael Knyszek <4473450dc5c88f06e1fb787f303d7805ec2aee65@google.com>
Run-TryBot: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>

golang/benchmarks,golang/benchmarks