undo CL 13180043 / 318540e7857f

Accidentally submitted.

««« original CL description
encoding/json: add "overflow" struct tag option

Fixes #6213.

R=golang-dev, dsymonds, bradfitz
CC=golang-dev
https://golang.org/cl/13180043
»»»

R=golang-dev
CC=golang-dev
https://golang.org/cl/13234045
5 files changed