undo CL 159990043 / 421fadcef39a

Dmitriy believes this broke Windows.
It looks like build.golang.org stopped before that,
but it's worth a shot.

««« original CL description
runtime: make pprof a little nicer

Update issue 8942

This does not fully address issue 8942 but it does make
the profiles much more useful, until that issue can be
fixed completely.

LGTM=dvyukov
R=r, dvyukov
CC=golang-codereviews
https://codereview.appspot.com/159990043
»»»

TBR=dvyukov
CC=golang-codereviews
https://codereview.appspot.com/160030043