Unit tests do still not use array but matrix by default

Now that #438 is merged, this passes. But with removing the filter as discussed  https://github.com/python-control/python-control/pull/438#discussion_r550271983 it seems that the actual new default is not set properly during the test suite run.

_Originally posted by @bnavigator in https://github.com/python-control/python-control/issues/486#issuecomment-752760149_