How do schools have the same number of each week day?
Make up days at the end of semester

The solution that I saw used is that for certain subjects, where one of "their" days fell on a holiday, the semester was one week longer, i.e. the break was shorter. Your described solution was not considered feasible - transferring a Friday class to Wednesday would fail because (a) there would be some students who have also chosen the Wednesday class and would have to be in two places at once; (b) there might be also a similar collision for lecturers who teach multiple classes and (c) there weren't enough facilities to host all the usual Wednesday classes plus all the usual Friday classes at once.

Skip them

Another reasonable possibility is to reduce the number of lectures. If it's known well in advance, it's no problem for a lecturer to take a course that usually is split in 14 lectures and teach it in 13 - and they can shift part of that material to extra reading and homework in the "empty" week where the lecture doesn't happen but students do have the rest of the week available.