Fix CODEOWNERS

[JelleZijlstra]

Fixes #1920

This version works, because I opened #1924 against this branch and it correctly requested review from Brett.

This makes three changes:

• revert Bisect CODEOWNERS to try and figure out why it isn't working #1921
• remove "Daniel Urban", whose name created a syntax error. I did some very brief searching and couldn't figure out what his GitHub username is.
• fix the path for the pep 418 directory

[brettcannon]

Thanks!

[pradyunsg]

Do we want to add a validation action here, given that this file breaks silently?

Originally suggested in #1920 (comment)

[brettcannon]

Probably, but I'm not sure how since I'm not aware of any official GitHub validation tool.

[pradyunsg]

https://github.com/mszostok/codeowners-validator seems like the best choice right now.

[brettcannon]

I'm honestly more worried about people forgetting to add new PEPs then breaking it with future updates. The format is simple enough that people adding themselves should generally work.