Fix social media section of splashpage

Commit e1e0bdb4 inadvertently added a 2nd version of the partial.

app/views/conferences/_social_media.haml

@@ -15,6 +15,9 @@
           - unless contact.googleplus.blank?
             = link_to "#{ contact.googleplus }" do
               %i.fa.fa-google-plus-square.fa-4x
+          - unless contact.mastodon.blank?
+            = link_to "#{ contact.mastodon }" do
+              %i.fa.icon-mastodon.fa-4x
           - unless contact.email.blank?
             = mail_to "#{ contact.email }" do
               %i.fa.fa-envelope-o.fa-4x

app/views/conferences/_social_media.html.haml

@@ -1,21 +0,0 @@
-.container
-  .row
-    .col-md-12.text-center
-      - unless @conference.contact.facebook.blank?
-        = link_to "#{ @conference.contact.facebook }" do
-          %i.fa.fa-facebook-square.fa-4x
-      - unless @conference.contact.twitter.blank?
-        = link_to "#{ @conference.contact.twitter }" do
-          %i.fa.fa-twitter.fa-4x
-      - unless @conference.contact.instagram.blank?
-        = link_to "#{ @conference.contact.instagram }" do
-          %i.fa.fa-instagram.fa-4x
-      - unless @conference.contact.googleplus.blank?
-        = link_to "#{ @conference.contact.googleplus }" do
-          %i.fa.fa-google-plus-square.fa-4x
-      - unless @conference.contact.mastodon.blank?
-        = link_to "#{ @conference.contact.mastodon }" do
-          %i.fa.icon-mastodon.fa-4x
-      - unless @conference.contact.email.blank?
-        = mail_to "#{ @conference.contact.email }" do
-          %i.fa.fa-envelope-o.fa-4x