You can remove the icon and the link by adding or updating a custom CSS file at /administrator/templates/isis/css/custom.css with the following CSS:
Note that the custom CSS option for administration templates was introduced in Joomla 3.4.1.
You can use the first parameter of addEntry() for that, for example:
public static function addSubmenu($submenu)
'<i class="icon-home"></i>' . JText::_('COM_SHOUTBOX_SUBMENU_SHOUTS'),
$submenu == 'shouts'
This would add the home icon to your menu ...
I haven't tried using an SVG as a favicon, but the addFavicon function is part of the JDocumentHTML class, therefore you should use it like so:
$path = JUri::root() . 'templates/MY_TEMPLATE/file.svg';
$type = 'image/svg+xml';
$rel = 'icon';
$doc = JFactory::getDocument();
$doc->addFavicon($path, $type, $rel);
You can try with one of this solutions:
Delete the line code
Go to your_site/administrator/templates/isis/login.php, here delete the code around line 130. Even so, the changes will be lost when you update the core, so it's more convenient the second option.
If you want to hide the joomla! icon in the login page and the joomla! icon in the ...
You are missing IcoMoon font or files are corrupted. Check into media/jui/fonts folder and see if IcoMoon files exist. If not, you can download them from Joomla! official github repository in here. Just upload those files to media/jui/fonts and it should fix that.
Maybe someone has accidently deleted font files. But it would be good to just override all ...