I found this adobe community post and it's working great.
Summary of the adobe answer: Layer > Layer Mask > From Transparency then edit the Layer Mask however necessary (Image > Adjustments > Threshold maybe).
But I have to do it everytime one by one.
Is there any smartfilter or effect that removes semi transparent pixels? So it can be applied to an smartobject and I don't have to make a new mask everytime the content of the smartobject changes?
If it's important: The content will have multiple colors. My testing with threshold (as a smartfilter) always reduced my colors to pure black.
Also I don't want to use an action, I know it would be possible with it, but because this will be shared with multiple co-workers, an action can lead to more errors than just a simple replacement of the smartobject content.
Here is an example, how an example image currently looks and how it looks after I did the steps mentioned above. Now I need something that would do this (if configured once) automatically.
My photoshop file: Download my Photoshop file from mediafire