devtools: remove unused bash

It is triggering scanning tooling inside Google and making them unhappy.

Change-Id: Idc88014b6583d7d94291b6723717ba354cb22ce6
Reviewed-on: https://go-review.googlesource.com/c/exp/+/561555
Auto-Submit: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Bryan Mills <bcmills@google.com>