In CL 206757 I added a log.Printf to identify when GOROOT is not read-only.
However, it interacts badly with test sharding in the builders:
the log is repeated for every shard.

Since the log statement isn't particularly high-value, just remove it.

Updates #30316

Change-Id: I385a7f35da59e38ad8b9beef92dc11af931d9571
Reviewed-on: https://go-review.googlesource.com/c/go/+/206898
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>