tests/events: remove the epub3 toc tests

These tests suffer from several issues:

  1.  The tests are not sourced, so it is unclear how representative
      of real-world usage they are. As a result, it is not possible
      to infer what a correct implementation should be.

  2.  The tests are not well-structured. This is because the ePub3
      navigation files belong in tests/epub3 as they test things
      from the ePub3 specs even though they are also valid HTML
      documents. Also, the tests are nav type=toc specific, but
      mix up toc and nav terminology.

As such, better tests will be created that address these issues.