Alt+F11, insert "Module", F5:

{{{
Sub RemoveUserNames()
Dim MyComment As Comment
Dim I As Integer
 
'Start looping through comments
   For Each MyComment In ActiveSheet.Comments
       
    'Find the position number of the Colon & LineFeed character combination
       I = InStr(1, MyComment.Shape.TextFrame.Characters.Text, ":" & vbLf)
       
    'Use the position number to reset the comment text to all but the user name
       If I > 0 Then
            MyComment.Shape.TextFrame.Characters.Text = _
            Mid(MyComment.Shape.TextFrame.Characters.Text, I + 2)
            MyComment.Shape.TextFrame.Characters.Font.Bold = False
        End If
       
'Go to the next comment
   Next MyComment
   
End Sub
}}}