Linear stepper shows edit icons instead of done icons

#### Bug:
Stepper shows edit icons instead of "done" icons

#### What is the expected behavior?
Completed steps should have a "done" icon on a linear stepper.

#### What is the current behavior?
Completed steps show an edit icon

#### What are the steps to reproduce?
https://angular-19juam.stackblitz.io
1. Fill step 1
2. Click Next
3. Notice icon on label

#### What is the use-case or motivation for changing an existing behavior?
The checkmark makes it easier to understand that a step is done. Perhaps the edit icon is still useful for `:hover` and `:focus`. Or perhaps the edit icon would work better on a non-linear stepper.

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Current build: 5.0.0-rc.3-05d726d

#### Is there anything else we should know?
On the issue #7260, it was marked as fixed but the stepper doesn't meet the material guidelines yet, and this is one of the reasons why.

Comienza con la reproducción vinculada de StackBlitz y sigue el stepper lineal después de completar el paso 1. Confirma que los pasos completados muestran un icono "done" en lugar de un icono de edición, teniendo en cuenta la nota del issue sobre el comportamiento al pasar el cursor y al recibir el foco. Done significa que el icono del paso completado coincide con el comportamiento esperado de Material Design.

Escrito por el modelo de indexación a partir del texto del issue.