Remove misleading translation comment

Also it was using the wrong field for translation comment.

src/gui/torrentcreatordialog.ui

@@ -291,7 +291,7 @@
       <item row="0" column="1">
        <widget class="QTextEdit" name="trackersList">
         <property name="toolTip">
-         <string comment="A tracker tier is a group of trackers, consisting of a main tracker and its mirrors.">You can separate tracker tiers / groups with an empty line.</string>
+         <string>You can separate tracker tiers / groups with an empty line.</string>
         </property>
         <property name="acceptRichText">
          <bool>false</bool>