removed x/twitter logo and links (#34)

Co-authored-by: David Zuckerman <dzuckerm@library.berkeley.edu>

Author: davezuckerman

app/assets/images/icons/twitter-square.svg

@@ -12,7 +12,6 @@
   </section>
   <section id="social-media">
     <a href="https://www.facebook.com/ucberkeleylibrary/"><%= image_tag('icons/facebook-square.svg', class: 'social-media-icon', alt: 'Facebook') %></a>
-    <a href="https://twitter.com/UCBerkeleyLib"><%= image_tag('icons/twitter-square.svg', class: 'social-media-icon', alt: 'Twitter') %></a>
     <a href="https://www.youtube.com/channel/UCrwP3Cw1FHwqslSAG5JkLTQ"><%= image_tag('icons/youtube-square.svg', class: 'social-media-icon', alt: 'YouTube') %></a>
     <a href="https://www.instagram.com/ucberkeleylibrary/"><%= image_tag('icons/instagram.svg', class: 'social-media-icon', alt: 'Instagram') %></a>
   </section>

app/views/layouts/_footer.html.erb

@@ -57,8 +57,6 @@ <h2>Record not found</h2>
   <section class="social-media">
     <a href="https://www.facebook.com/ucberkeleylibrary/"><img class="social-media-icon" alt="Facebook"
                                                                src="/assets/icons/facebook-square.svg"/></a>
-    <a href="https://twitter.com/UCBerkeleyLib"><img class="social-media-icon" alt="Twitter"
-                                                     src="/assets/icons/twitter-square.svg"/></a>
     <a href="https://www.youtube.com/channel/UCrwP3Cw1FHwqslSAG5JkLTQ"><img class="social-media-icon" alt="YouTube"
                                                                             src="/assets/icons/youtube-square.svg"/></a>
     <a href="https://www.instagram.com/ucberkeleylibrary/"><img class="social-media-icon" alt="Instagram"

public/404.html

@@ -56,8 +56,6 @@ <h2>We're sorry, but something went wrong.</h2>
   <section class="social-media">
     <a href="https://www.facebook.com/ucberkeleylibrary/"><img class="social-media-icon" alt="Facebook"
                                                                src="/assets/icons/facebook-square.svg"/></a>
-    <a href="https://twitter.com/UCBerkeleyLib"><img class="social-media-icon" alt="Twitter"
-                                                     src="/assets/icons/twitter-square.svg"/></a>
     <a href="https://www.youtube.com/channel/UCrwP3Cw1FHwqslSAG5JkLTQ"><img class="social-media-icon" alt="YouTube"
                                                                             src="/assets/icons/youtube-square.svg"/></a>
     <a href="https://www.instagram.com/ucberkeleylibrary/"><img class="social-media-icon" alt="Instagram"