You'll need to remove the ability to log in from two places - your layout.html file and your _columns_2.html file. 

In layout.html remove this (depending on changes you've already made it should be around line 160):

{% else %}
Sign in with <a href="{{ request.facebook_connect_url }}">Facebook</a>, <a
href="{{ request.twitter_connect_url }}">Twitter</a> or <a href="/login">email</a>.

In _columns_2.html remove this (around line 24):

<div class="signin-wrap">

<h3>Sign in with:</h3>
<ul class="supporter-nav-signin">
<li><a href="{{ request.facebook_connect_url }}"><i class="fa fa-facebook"></i></a>
</li>
<li><a href="{{ request.twitter_connect_url }}"><i class="fa fa-twitter"></i></a></li>
<li><a href="/login"><i class="fa fa-envelope"></i></a></li>
</ul>

{% if request.sorta_logged_in? %}
{% else %}
<h3>Or sign up:</h3>
{% endif %}
{% if site.has_signup_page? %}
{% include "signup_form" with site.signup_page %}
{% endif %}

</div>