google-api-go-client: remove JSON shim type hack
google-api-go-client: remove JSON shim type hack

R=bradfitz, dave
CC=golang-dev
https://codereview.appspot.com/9807044

Committer: Francesc Campoy <3149fa091f5edfa916be664d7a800f2d780f07b1@golang.org>

abujehad139/google-api-go-client,tmaiaroto/google-api-go-client,freehaha/freehaha-gapi,tmaiaroto/google-api-go-client,Shino1024/google-api-go-client,abujehad139/google-api-go-client,Shino1024/google-api-go-client,freehaha/freehaha-gapi,maskofG/google-api-go-client,aquarat/google-api-go-client,aquarat/google-api-go-client,maskofG/google-api-go-client