Remove deprecation of the old FileUploadSupport

### Guice users need the old FileUploadSupport

`org.scalatra.fileupload.FileUploadSupport` lets the Guice ServletModule users to handle multipart
uploads, whereas `org.scalatra.servlet.FileUploadSupport` does not.

Guice ServletModule does not work with the Servlet 3 multipart-parser implementations of Jetty 8 and Tomcat 7. This seems the be caused by the way Guice interacts with the servlet container: Guice handles HTTP requests in the filter context, while Jetty and Tomcat expect multipart requests to be handled within the servlet context.

#### Summary

I could not get Jetty or Tomcat to handle multipart uploads when I used `org.scalatra.servlet.FileUploadSupport` with Guice-configured Scalatra servlets. Consequently, I propose that we remove the `@Deprecation` status from `org.scalatra.fileupload.FileUploadSupport`.