This reverts commit 7365fac2.

Reason for revert: breaks the build on some architectures, reading unmapped pages?

Change-Id: I3a8c02dc0b649269faacea79ecd8213defa97c54
Reviewed-on: https://go-review.googlesource.com/97995Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>