It will require to delete the following fragment from your Splash block code:

<div class="bx-spl-cell bx-spl-c2 bx-hide-when-logged-in">

       <div class="bx-spl-ccnt bx-def-padding">__join_form_in_box__</div>

</div>

This block can be found in Studio->Pages->System->home page area. Just click the necessary block, cut the mentioned part and press "Save" button.