Remove system test delzone

Remove system test delzone

There are multiple reasons to remove this test as obsolete:

- The test may not possibly work for over 2.5 years, since
  98b3b93791777218c04a67ddaef22619162249f7 removed the rndc.py python
  tool on which this test relies.
- It isn't part of the test suite either in CI or locally unless it is
  explicitly enabled. As a result, there are many issues which prevent
  the test from being executed caused by various refactoring efforts
  accumulated over time.
- Even if the test could be executed, it has no clear failure condition.
  If the python script(s) fail, the test still passes.

(cherry picked from commit 05180154d9742954e1675b687db9bd8387664eb3)