If you found the link in a backup file, then you should be able to figure out what table and column it's in. If you tell us that, we should be able to tell you where you can change it in the admincp. Or at least it would be easier to find where to edit it in phpMyAdmin.
Be careful of what you edit directly in the database. If you edit a text field which is in serialized format you can make it invalid. If at all possible you should have a current backup before making changes.
I'm not sure how to tell you which table or column it is in. I just opened the sql file on wordpad and used the search option to find the link. Sending you a screenshot in the PM showing you what I found in the wordpad.
ECZ ... you can get to that http link directly from your admin panel ... go to your templates and just type in the any of the following and do a search:
<script type="text/rocketscript">
var pkBaseURL = (("https:" == document.location.protocol) ? "https://yourdomain.com/analytics/piwik/piwik/" : "http://yourdomain.com/analytics/piwik/piwik/");
document.write(unescape("%3Cscript src='" + pkBaseURL + "piwik.js' type='text/javascript'%3E%3C/script%3E"));
</script><script type="text/rocketscript">
try {
var piwikTracker = Piwik.getTracker(pkBaseURL + "piwik.php", 1);
piwikTracker.trackPageView();
piwikTracker.enableLinkTracking();
} catch( err ) {}
</script><noscript><p><img src="http://yourdomain.com/analytics/piwik/piwik/piwik.php?idsite=1" style="border:0" alt=""/></p></noscript>
Just type in anything from that script and you should find it in one of the templates my Man ... no need to go into your database at all ...
--------------- Added 1436363339 at 1436363339 ---------------
I would do a search for this:
analytics/piwik/piwik/piwik
and you should have no problem finding it ..
I tried searching like this. Didn't find anything. I didn't know Piwik was causing trouble too for SSL. I thought it was just that one image being loaded as http.