Remove authors field from all the manifests

[lf-]

Since RFC3052 is fully implemented in Cargo and the various Rust
websites, we can set an example by removing the authors field from all
the listings as it has been effectively soft deprecated since the last edition
of the book.

Follow on/related to #2785, which removed the references in the text.

[carols10cents]

THANK YOU so much for this!!! I was dreading writing a script :)

[lf-]

THANK YOU so much for this!!! I was dreading writing a script :)

I did find . -name 'Cargo.toml' -exec sed -Ei '/authors =/d' '{}' ';' to do the edit, in case you end up with a similar text editing job in the future :)

[carols10cents]

Thank you!!!! sed and I usually have lots of disagreements about regex matching when I try to do something like this ;)