The following files added utf-8 encoding but never used. So we can
removes them at all.
ironic_python_agent/extensions/image.py
ironic_python_agent/extensions/iscsi.py
ironic_python_agent/tests/unit/extensions/test_image.py
ironic_python_agent/tests/unit/extensions/test_iscsi.py
Change-Id: Ifc98faf025ee81f885ea58d9203037c6357ea7f2