Remove authors manifest field

[lnicola]

• [x] I agree to follow the project's code of conduct.

• [ ] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

r? @nyurik

[nyurik]

I'll let @urschrei take a look at it first since they changed it last

[lnicola]

bors r=nyurik,urschrei

[bors[bot]]

Build succeeded:

• wkt