Makefile: Remove `make world` and `make kernel`

[emaste]

Summary

make world was deprecated more than two decades ago and is a bad and dangerous approach. Belatedly remove it.

[ziaee]

Sir when you merge this please note that I disapproved. This code is not causing any problems.

[emaste]

There are a few handbook references to make world. Some of them are bad - e.g.

it is possible to compile the entire operating system just by typing make world in the appropriate directory!

[ziaee]

When I was a kid, I was in awe by the unbelievable simplicity and elegance of that statement.

[emaste]

But that statement is not correct, it is missing "and overwrite the running system" after "compile"

[emaste]

Also make kernel

[ziaee]

If you want to remove them from build(7) so the commit is atomic for our downstream, I have no problem resolving the conflict in my build(7) draft.

[emaste]

update build(7)

[ziaee]

This also needs to be in UPDATING and Relnotes, I think, since it is a breaking change of decades of behavior.