Remove drupal connector dependency from composer.json

Otherwise you'll get the below issue:

````
$ composer update
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for liip/drupal-testing dev-master -> satisfiable by liip/drupal-testing[dev-master].
    - liip/drupal-testing dev-master requires liip/drupalconnectormodule dev-master -> no matching package found
.

Potential causes:
 - A typo in the package name
 - The package is not available in a stable-enough version according to your minimum-stability setting
   see <https://groups.google.com/d/topic/composer-dev/_g3ASeIFlrc/discussion> for more details.

Read <http://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.
````