Fix deprecation comments in rpc_util.go

[dnephin]

The golang convention for deprecating functions is to use Deprecated:. Most deprecated functions in this repo follow the convention, however a few in rpc_util.go use Deprecated; (semicolon).

This PR fixes the comment string so that staticcheck will correctly recognize the function as deprecated.

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[dfawley]

This can't be done until gRPC itself stops using the deprecated functions. If you would like to make those changes as well, we can approve them; otherwise, we will wait until we have the cycles to do that.

[dnephin]

I've updated 2 of 3. I'll try and get the last one sometime soon.

[dnephin]

The build failure on go1.9 seems unrelated, but I'm not sure. I think this is ready for a review

[dfawley]

The build failure on 1.9 is the gofmt check failing -- can you rerun it please? This also needs a rebase to resolve the conflict in balancer_switching_test.go Thanks!

[dnephin]

Fixed the conflicts, build is green

[dfawley]

Nice, thanks for seeing this through!