go/types: use the same interface method sorting as types2

go/types: use the same interface method sorting as types2

See also CL 321231 which introduces object.less to match
expected compiler behavior.

Change-Id: I56fbf332a04596dc96393b71d40acf4df5d950fd
Reviewed-on: https://go-review.googlesource.com/c/go/+/461677
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>