[3.0] Removed all $that variables

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | maybe
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~
It's meant to be merged into 3.0 where BC breaks are allowed.