Remove 'delegate_method' matcher

* See issue #252
Remove 'strong_parameters' matcher

* See issue #252
* Also changes bourne dependency into a development dependency
Remove 'have_sent_email' matcher

* See issue #252
Remove 'validate_format_of' matcher

* See issue #252
Remove 'query_the_database' matcher

* See issue #252
Remove 'respond_with_content_type' matcher

* See issue #252
Remove 'assign_to' matcher

* See issue #252
Mention matcher removals in NEWS.md