Every few months we get a new error report claiming that there
is a typo in the spec related to this specific example. Clearly,
the fact that two types with the same identifier are identical
seems exceedingly obvious to readers; thus the example seems not
worth the trouble. Removing it.

For #9226.
For #22202.
For #22495.
For #23096.
For #23409.

There may be more.

Change-Id: I003ba79dc460ffb028a4ecb5f29efd60f2551912
Reviewed-on: https://go-review.googlesource.com/87417Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>