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.

Commencez par la reproduction StackBlitz liée et suivez le stepper linéaire après avoir terminé l'étape 1. Vérifiez que les étapes terminées affichent une icône "done" plutôt qu'une icône de modification, tout en tenant compte de la remarque de l'issue concernant le comportement au survol et au focus. Done signifie que l'icône de l'étape terminée correspond au comportement attendu de Material Design.

Rédigé par le modèle d'indexation à partir du texte de l'issue.