The version of pprof in gperftools has been deprecated.
No need to have a pointer to that version since go tool pprof
is included with the Go distro.

Change-Id: I6d769a68f64280f5db89ff6fbc67bfea9c8f1526
Reviewed-on: https://go-review.googlesource.com/24509Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>