* append contents of race1.go to race.go
* delete "Implementation of the race detector API." comment
  from race1.go

Updates #12952

Change-Id: Ibdd9c4dc79a63c3bef69eade9525578063c86c1c
Reviewed-on: https://go-review.googlesource.com/16023
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>