Revert "Add test cases for the IResourceModification plugin interface"

This reverts commit 9f034dcff42ffeccca63a8ec835897a184e1f4ea.

The commit added tests to the "old" version of tests which has now
been deprecated and new_tests should be used instead of it.
Add example plugin implementation and tests for IResourceModification

This adds an example ckan extension that uses the IResourceModification
plugin interface and then adds three tests for that example
implementation:

* One test case for before_create and after_create
* One test case for before_update and after_update
* One test case for before_delete and after_delete