Code cleanup. Removed not used namespaces/using

[SychevIgor]

In the code was a lot of not used namespaces. It's minor changes in the code without any kind backward compatibility issues.

[Mpdreamz]

Hi @SychevIgor

Thank you for taking the time to submit a PR but sadly I can't pull this in:

We have set Resharper to never automatically remove common system namespace references, see this similar PR for more background:

#758

As such I can't pull this in and am not likely to pull any future namespace cleanup commits that are not part of a bugfix/new feature change.

Thats not to say we wont accept other cleanup commits but please open a ticket if something bothers you stylistically first 👍

Can you sign the Elasticsearch CLA: http://www.elasticsearch.org/contributor-agreement/ that way we are allowed to pull in any future PR's from you :)

[SychevIgor]

Agreement is signed.

In fact it's not stylistics in my particulate case. We are experimenting with api now and build of the project was integrated in Continuous Integration process. One step of the build is static code analysis. Based on our default rule set usings/namespaces are must be used or not presented in the code. There were 1000+ warning from this and we want to fix and observe other potential issues without such a noise.

As I see now - building CI process is not compatible with our default rules and it's easy just save the code on a disk and don't care about build process because it will take a lot of time.