Google launched the awesome manual actions viewer just about 11 months ago and it is really an awesome step in visibility around penalties (yes we are waiting for an automated actions viewer).
Here you can quickly tell if a site that you have verified access to has a Google manual action and if so, what kind.
So if you get an email from Google or what appears to be from Google about a penalty, check there. You cannot delete manual actions without the manual action being revoked through a reconsideration request or automatically expiring by themselves. The manual action won't just disappear if your penalty is still there.
So don't be fooled by fake emails, check the manual action viewer. Of course, algorithmic actions won't show there but Google won't send you an email about those penalties anyway.
One Google Webmaster Help thread has someone claiming an employee of his deleted the manual action but he still has the penalty. That is not possible, as far as I know. There is no delete button. Here is a screen shot:
So don't be fooled. There is no delete button, as of yet.
Forum discussion at Google Webmaster Help.
