Have script_helper._assert_python strip refcount strings from stderr.
Have script_helper._assert_python strip refcount strings from stderr.

This makes the output of the function and those that depend on it
independent of whether or not they are being run under a debug
build.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator