support/testing/tests: drop Python 2.x test in test_ipython

support/testing/tests: drop Python 2.x test in test_ipython

Since commit 6ebaef3818d6e3dc821616a33391eb6d594a053e
("package/python-ipython: bump to version 7.4.0"), ipython is no
longer available for Python 2.x, as it requires Python 3.x.

However, the corresponding test case that was testing iPython under
Python 2.x was not removed at the same time, causing a failure of
TestIPythonPy2 test. Let's drop the test that is no longer relevant.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/210208754

Cc: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>