Also remove some of the now unnecessary corner case handling and
tests I've been adding recently for unexported method data.

For #15673

Change-Id: Ie0c7b03f2370bbe8508cdc5be765028f08000bd7
Reviewed-on: https://go-review.googlesource.com/23410Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>