remove &mut PoolConnection from Executor docs

[olback]

As per the Changelog for the 0.7.0 release:

The Executor impls for Transaction and PoolConnection have been deleted because they cannot exist in the new crate architecture without rewriting the Executor trait entirely.

[olback]

The failing CI fmt check isn't due to any of my changes, should I fix it anyway?

[ShayBox]

How do I fix this in my code? I use conn: &mut PoolConnection<MySql> everywhere in my library which has to work with sqlx and rocket_db_pools. I can't seem to use &Pool, MySqlConnection, or AnyConnection.

[abonander]

Dereference the PoolConnection: &mut *conn