test/py: don't import pexpect

The code replaced pexpect with custom code long ago. Don't import the
unused module so it doesn't need to be installed.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

test/py/conftest.py

@@ -17,7 +17,6 @@ import atexit
 import errno
 import os
 import os.path
-import pexpect
 import pytest
 from _pytest.runner import runtestprotocol
 import ConfigParser