Fix: Convert row->columns in hw4.jl

[hydrosquall]

Motivation

While working on Hw4, the caption seemed out of sync with the behavior.

From comparing the first and last image, we can see that the last image is made up of the last 2 columns of the first image.

We would need a remove_in_each_column function to remove the first 2 rows, the current function can only remove 1 item per row per pass.

The current behavior removes the first 2 columns, not rows .

[fonsp]

Thanks!!