crypto/cipher: add small CTR benchmark, remove CFB/OFB benchmarks
CFB and OFB are mostly unused, and not a performance target.
Updates #39365
Updates #69445
Change-Id: Ice6441e4fee2112a9e72607c63e49dbc50441ba6
Reviewed-on: https://go-review.googlesource.com/c/go/+/621957 Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>