sweet/harnesses: stop trimming "devel " prefix from Go version

The "devel " prefix is no more as of CL 668015. It's still present as
a substring, making it a https://go.dev/doc/toolchain#name compatible
format (a "non-standard toolchain").

For golang/go#73369.

Change-Id: I86693562119bf7ec8f61a2fab902b29ceaefede3
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/669215
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>