Revert "go/types, types2: consider shared methods when unifying against interfaces"

Revert "go/types, types2: consider shared methods when unifying against interfaces"

This reverts commit c4afec232cec72ce030139ae2772450fad89f188.

Reason for revert: submitted accidentally via auto-commit

Change-Id: Idbfd90a4f1c2d582d86fc8aa45e037c406adbd40
Reviewed-on: https://go-review.googlesource.com/c/go/+/497655
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>