hi, you can edit the NAML code. click on "edit this page", search for the macro "last_post_column_start"
you will see:
<override_macro name="last_post_column_start">
<n.overridden/>
<td style="padding:0;vertical-align:top;border:none;">
<n.owner.avatar size="small"/>
</td>
</override_macro>
remove the lines between the "override_macro" tags , the avatar will be removed...