cmd/dist: remove pkg/$GOOS_$GOARCH and pkg/obj at exit
pkg/obj will be empty, so just remove it.
pkg/$GOOS_$GOARCH will be empty unless the user has specified
GODEBUG=installgoroot=all, so check if it's empty, and if so, delete
it.
Also remove xreaddirfiles, which is unused.
Also remove the copy of pkg/$GOOS_$GOARCH in the cmd/go test
TestNewReleaseRebuildsStalePackagesInGOPATH. The directory is empty so
copying it has no effect.
For #47257
Change-Id: Ief90b882d157bd16078cd5d2b83a915bfc831f9a
Reviewed-on: https://go-review.googlesource.com/c/go/+/453496
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Matloob <matloob@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>