The Makefiles and includes and code for the original "schar" device example have been outdated by some changes in at least some of the linux releases. Debian for sure no longer works. I don't know what the exact changes are but it seems that it might have fragmented how to write kernels.
Some writing by the authors explaining why they dropped that chapter would be helpful. Even in the older editions, the schar device was one of the more complicated and involved examples. There are some books that focus just on writing device drivers for linux. It could be that it was just too complicated and fragmented to be useful.
However, I do agree with the sentiment that it was an important part of the original book. Even if one never writes a driver, having how the kernel interacts with the devices was very enlightening.