Remove AdminAnalytics Adobe tracking URL

This change ensures that in case the tracking-feature is enabled
in the admin, Mage-OS will not be tracked as Magento Open Source
or Enterprise Edition installations incorrectly.

In order to use admin analytics, a custom tracking_url script needs to
be configured on the tracking block.

Fixes #43

app/code/Magento/AdminAnalytics/view/adminhtml/layout/default.xml

@@ -10,7 +10,8 @@
         <referenceContainer name="header">
             <block name="tracking" as="tracking" template="Magento_AdminAnalytics::tracking.phtml" ifconfig="admin/usage/enabled">
                 <arguments>
-                    <argument name="tracking_url" xsi:type="string">//assets.adobedtm.com/a7d65461e54e/37baabec1b6e/launch-177bc126c8e6.min.js</argument>
+                    <!-- For Mage-OS the tracking_url is empty by default. -->
+                    <argument name="tracking_url" xsi:type="string"/>
                     <argument name="metadata" xsi:type="object">Magento\AdminAnalytics\ViewModel\Metadata</argument>
                 </arguments>
             </block>