The comments about pcln functions are obsolete since those functions
now live in cmd/internal/obj. The copyright header is redundant with
the existing one at the top of the file.

Change-Id: I568fd3d259253a0d8eb3b0a157d008df1b5de106
Reviewed-on: https://go-review.googlesource.com/31315Reviewed-by: Ian Lance Taylor <iant@golang.org>