I believe that a component overrides the template files as you discovered.
So - your solutioncould be:
a) custom plugin development to remove said files. Here's a discussion: How can I completely remove Bootstrap from the frontend of Joomla?
b) Modify the jdoc:include type=head in your Joomla Template:
c) I use JCC - JS CSS Control plugin - which is the most reliable and simplest way I have found.
I encounter the issue with flexiContent + RSform - so keep my own adaptation:
https://gist.github.com/iamrobert/a1316f598a1acc745fec8cc81d866044
As you're seeking the administrator - I would search the module folder for the line of code and comment it out.
As I don't use K2, I looked at the mod_k2_Stats and found the following in the tmpl folder - so it could be removed:
if (K2_JVERSION == '30') {
$document = JFactory::getDocument();
$document->addStyleDeclaration('
dl.tabs {float:left;margin:10px 0 -1px 0;z-index:50;}
dl.tabs dt {float:left;padding:4px 10px;border:1px solid #ccc;margin-left:3px;background:#e9e9e9;color:#666;}
dl.tabs dt.open {background:#f9f9f9;border-bottom:1px solid #f9f9f9;z-index:100;color:#000;}
div.current {clear:both;border:1px solid #ccc;padding:10px 10px;background:#f9f9f9;}
dl.tabs h3 {font-size:12px;line-height:12px;margin:4px;}
');
}
Or in mod_k2_quick_icons:
K2HelperHTML::loadHeadIncludes(true, false, true, false);
if ($modCSSStyling) {
$document->addStyleSheet(JURI::base(true).'/modules/'.$mod_name.'/tmpl/css/style.css?v='.K2_CURRENT_VERSION);
}
Or in other non k2 modules:
$url = 'modules/mod_adminmenumanager/javascript/responsive.js';
$document->addScript($url);
or
echo "<script>window.parent.addtomenu_setMessage( '" . JText::_('COM_MENUS_MENU_ITEM_SAVE_SUCCESS', true) . "', 1 );</script>\n";