Post Lab 29
Write a function remove_non_numeric(opened_file), which takes
an opened file as a parameter. Your function should return a list of lines
from the file which contain only numeric digits. Your list should
contain strings which are just the numeric digits, and should have
all extraneous whitespace removed.
from io import StringIO # DO NOT REMOVE. NEEDED FOR TEST CASES
def remove_non_numeric(opened_file):