cdkTextareaAutosize should remove cdk-textarea-autosize on disabled

#### Reproduction

https://stackblitz.com/edit/angular-5x8mff

Steps to reproduce:
1. set `cdkTextareaAutosize` to false


#### Expected Behavior

When passing a false value to `cdkTextareaAutosize` I would expect to be rendered as a simple textarea.

- `rows` should be unset
- `cdk-textarea-autosize` should be removed

#### Actual Behavior

- `rows` set 1
- `cdk-textarea-autosize` is set.

#### Environment

- Angular: `8.2.14`
- CDK/Material: `8.2.3`
- Browser(s): `Chrome`
- Operating System (e.g. Windows, macOS, Ubuntu): `macOS`

Start with the linked StackBlitz reproduction and trace the cdkTextareaAutosize behavior when its input is false. Done means a disabled autosize textarea behaves as a simple textarea: rows is unset and the cdk-textarea-autosize class is removed.

Written by the indexing model from the issue text.