internal/concurrent: remove dependency on math/rand/v2
This change uses linkname for the one random function
internal/concurrent needs to avoid taking a dependency on math/rand/v2.
This lowers the bar to using this package.
Change-Id: I9dba1121b66ba35f56521643937f220936ea5321
Reviewed-on: https://go-review.googlesource.com/c/go/+/594057 Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>