I see this question got migrated. To try to answer it again...
When you deauthorize an app in your Facebook application settings, you have the option of deleting posts made by that app. Click the "X" to the far right of the application listing, then choose "Delete all app activity".
The original answer from Stack Overflow was:
In general, you can go through your timeline by looking at:
For each entry, find the ones whose application ID matches the app in question, and then delete them.