forumlist_body.html (prosilver) (back up that file first)
comment line 19 and 20 to remove column headers
<dd class="topics">{L_TOPICS}</dd>
<dd class="posts">{L_POSTS}</dd> comment line 79 and 80 to remove the counts
<dd class="topics">{forumrow.TOPICS} <dfn>{L_TOPICS}</dfn></dd>
<dd class="posts">{forumrow.POSTS} <dfn>{L_POSTS}</dfn></dd>
Disclaimer: this was just a quick search and test on prosilver 3.3.11 (I might have missed something).
BTW: in most cases using your browser's Inspector mode allows you to edit the page build and view the result without touching the phpBB files: that way you can easily identify the sections to edit.
Spelling is freeware, which means you can use it for free.
On the other hand, it is not open source, which means you cannot change it or publish it in a modified form.
Time flies like an arrow, but fruit flies like a banana.