examples: README: remove sh tags
examples: README: remove sh tags

The markdown renderer for grpc.io doesn't know what to do with the tags
with the syntax highlighting tag like:

```
```sh
```

See http://www.grpc.io/docs/installation/go.html

mpl/grpc-go,hugoz1234/grpc-go,improbable-io/grpc-go,rakyll/grpc-go,andreimatei/grpc-go,go4org/grpc,grpc/grpc-go,stanley-cheung/grpc-go,mpl/grpc-go,bradfitz/grpc-go,luan-cestari/grpc-go,MakMukhi/grpc-go,dsymonds/grpc-go,cuiweiqiang/grpc-go,hugoz1234/grpc-go,rakyll/grpc-go,andreimatei/grpc-go,iamqizhao/grpc-go,cuiweiqiang/grpc-go,MakMukhi/grpc-go,fuchsia-mirror/third_party-grpc-grpc-go,bradfitz/grpc-go,abhishekgahlot/grpc-go,s4uliu5/grpc-go,grpc/grpc-go,improbable-io/grpc-go,stanley-cheung/grpc-go,Sajmani/grpc-go,luan-cestari/grpc-go,peter-edge/grpc-go,dfawley/grpc-go,menghanl/grpc-go,djs55/grpc-go,menghanl/grpc-go,thinkerou/grpc-go,dfawley/grpc-go,Sajmani/grpc-go,iamqizhao/grpc-go,thinkerou/grpc-go,s4uliu5/grpc-go,dsymonds/grpc-go,abhishekgahlot/grpc-go,djs55/grpc-go,fuchsia-mirror/third_party-grpc-grpc-go,go4org/grpc,peter-edge/grpc-go