Rearrange Dead Code prep and backlog

[Poonam-raj]

Which module(s) and week(s) does this change affect?
Module(s): 1 and 3
Week(s): 7 (Module 1 sprint 3) and 14 (module 3, last sprint)

What is the work that needs to be done?

Move Dead Code prep material, backlog item and backlog exercises to Module 1 sprint 3.
Original issue here: #1592 (comment)

Why is this work important to do?

More logical and earlier placement of refactoring skill learning.

Who might need to know about this change?

@Poonam-raj @illicitonion