Revert "2012: fix mix-up of semantic/syntactic"

This reverts commit fbdfadebf1193ff057da2c1ca46db54437d0c9b1.

Reason for revert: The original is correct. It says both the old and new are syntactically good, so therefore it's semantics that change.

Change-Id: Iee019438eaa9afd7dac2862b36fae24b040d6ffb
Reviewed-on: https://go-review.googlesource.com/49730
Reviewed-by: Rob Pike <r@golang.org>