goprotobuf: update for new delete syntax.
goprotobuf: update for new delete syntax.

R=dsymonds
CC=golang-dev
http://codereview.appspot.com/5302070

tamird/protobuf-2,jmptrader/protobuf-1,jeremyletang/protobuf,linkedin-inc/protobuf,skyportsystems/go-protobuf,tamird/protobuf-2,trdata/protobuf,fuchsia-mirror/third_party-github.com-golang-protobuf,velocity-toolkit/protobuf-1,csuideal/protobuf,ekle/protoc-gen-goweb_test,skyportsystems/go-protobuf,qinlodestar/protobuf,mwitkow-io/protobuf,golang/protobuf,ekle/protoc-gen-goweb,hailocab/protobuf,kung-foo/protobuf,trdata/protobuf,golang/protobuf,fuchsia-mirror/third_party-github.com-golang-protobuf,alskjstl/protobuf,jrbarron/protobuf,francoishill/protobuf,aoeu/protobuf,daemonl/protobuf,ArtemTeleshev/go-protobuf,adnaan/protobuf,eduardiazf/protobuf