Write a function named scale_by_k that accepts a list of integers as a parameter and replaces every integer of value k with k copies of itself. For example, if the list stores the values [4, 1, 2, 0, 3] before the function is called, it should store the values [4, 4, 4, 4, 1, 2, 2, 3, 3, 3] after the function finishes executing. Zeroes and negative numbers should be removed from the list by this function.