I would only consider "deleting" the 4 x 5 enlarger if:

a) you have all the necessary parts to enlarge everything between 6 x 6 and 5 x 7 using the 5 x 7 enlarger, and
b) removing one enlarger would free up space, and you could use that space.

6 x 6 enlargers are usually more convenient for 35mm and smaller formats than 4 x 5 and 5 x 7 enlargers, so I wouldn't get rid of the 6 x 6 enlarger.

And the 5 x 7 enlarger is the only one big enough for 5 x 7 or panoramic formats like 6 x 17.