Remove redundant author IDs from existing CIPs and template

[rootulp]

Context

my only nit would be a question of whether or not we're going to change this on CIPs?

Yea can do. We can also update the template to include just Github username.

Originally posted by @rootulp in https://github.com/celestiaorg/CIPs/issues/272#issuecomment-2733627752

Problem

Existing CIPs and the template have multiple IDs for authors.

Proposal

1. Remove redundant author IDs from existing CIPs. Preserve Github username, remove names and emails
2. Repeat that for the CIP template