[dev.cmdgo] cmd/go: clean up TODOWorkspaces instances

Address some of the easier todos to address and remove the todos that
have already been done and redundant todos.

For #45713

Change-Id: I3fe4393168b10c6e005325258d9701713c92e9e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/344491


Trust: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>