qt: remove fee recommendation in settings

This value gets stale really quickly, do not hardcode it into a message.
Completely remove it for now.
Later on, a mechanism will be added to determine fees based on the mempool.

Closes #2576

src/qt/forms/optionsdialog.ui

@@ -33,7 +33,7 @@
        <item>
         <widget class="QLabel" name="transactionFeeInfoLabel">
          <property name="text">
-          <string>Optional transaction fee per kB that helps make sure your transactions are processed quickly. Most transactions are 1 kB. Fee 0.01 recommended.</string>
+          <string>Optional transaction fee per kB that helps make sure your transactions are processed quickly. Most transactions are 1 kB.</string>
          </property>
          <property name="textFormat">
           <enum>Qt::PlainText</enum>