Remove `update_server_branch.sh` script

Use the more configurable form of the `update_server_branch.sh`
script the has been added in a separate repository.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Note: The `update_server_branch.sh` was moved into a different
repository in order to:

 * be more easily maintained
 * allow other projects with similar needs to use it
   (e.g.: https://github.com/h5bp/html5boilerplate.com-mobile)