TST: Remove broken test for deprecated functionality
Registering converters by default on import is deprecated since #28722.

The test did not fail as the subprocess call contains errors in the python code. Specifically, the code is in double and single quotes. This means that the python code passed to the subprocess call is never actually excecuted. Python in the subprocess is called to "excecute" a string. This is will simply finish with exit code 0 as there is nothing to do basically.
Additonally, the test code contains a stray closing bracket at the end which would make the code fail if it was excecuted. 

- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
