Remove trailing whitespace and incorrect comment

I've run https://stackoverflow.com/a/5130044/15544350 and [zsh] perl -pi -e 's/ +$//' **/* on the whole codebase to remove trailing whitespace, which messed with my git diffs during development.

I've also removed an incorrect comment remaining from stanford, which says that busy wait is unacceptable and must be fixed (which is not a part of this course). This comment confused me when I delved into the code and caused me to spend some time on learning how the waiting works.

This request should probably not be merged until the course is finished, or students might get horrible merge conflicts. I merged it into my code base and it still worked, but you should likely do it as well to double check that I haven't accidentally broken something.

There's a couple files with curled braces on the same row, though I didn't bother fixing that. But whoever wrote lab13/os.c quite consistently haven't stuck to having them on a separate row as is the convention in the rest of the files :^)

Thanks for a fun lab series!