undo CL 5375043 / ea8b178f9b73

Never lasts long.

««« original CL description
gc: add GOEXPERIMENT=reorg

This won't last long but may ease conversions.

R=ken2
CC=golang-dev
https://golang.org/cl/5375043
»»»

R=ken2, ken
CC=golang-dev
https://golang.org/cl/5370043