Clarify auto usage.

[bruvzg]

- Remove outdated #pragma once note, it is now preferred style.

• Changes auto notes to reflect actual state of the codebase (it is used a lot in two mentioned scenarios).

[skyace65]

There's an existing PR open for pragma once that covers more #10756. Any review on that would be appreciated,

Other than the one issue I found the auto keyword stuff looks good.

[bruvzg]

There's an existing PR open for pragma once that covers more #10756.

Reverted this part.

[skyace65]

Thanks!