remove top level turnitintool directory

Including the `turnitintool` directory does not conform to Moodle plugin standards. Instead, the turnitintool directory should be created by the end user during install. You can also reference this template: https://github.com/moodlehq/moodle-mod_newmodule

Furthermore, by removing the turnitintool top directory in this repository, others can reference this plugin as a submodule through git. As it stands, one cannot link to this project as a submodule because the directory structure is incorrect.