BIP2 states that the Discussions-To header should only be used if the
proposal was discussed somewhere else beside the Bitcoin Developer
Mailing List. Therefore, the only use of the Discussions-To header in
the repository is unnecessary and can be removed before the header is
abolished.
```
sed -z -i 's/Author: /Authors: /' bip-0*.md
sed -z -i 's/Author: /Authors: /' bip-0*.mediawiki
```
Also align correctly in case of multiple authors.
```
sed -z -i 's/Type: Standards Track/Type: Specification/' bip-0*.md
sed -z -i 's/Type: Standards Track/Type: Specification/' bip-0*.mediawiki
```
After the scripted changes, the changes to BIP-40, BIP-41, and BIP-63
were undone, because it breaks CI.
These three BIPs only exist conceptually and their proposal documents
are missing which causes changes to them ot break the CI. I defer the
changes to these BIPs to a separate pull request to get CI to pass.
