In the skin directory you wish to edit, find the UIFILE 923, contains the elements. Around line 181 you should see this line of code:
code:
<Element layoutpos=bottom layout=borderlayout() padding=rect(4,0,4,0)>
Change the layoutpos to make the element invisible, by replacing it with this:
code:
<Element layoutpos=none layout=borderlayout() padding=rect(4,0,4,0)>
That should remove the ad from Messenger. Of course the skin may have saved the UIFILE in different names or the code may be one a different line
.