Remove references to twitter.com/include_cpp

Co-Authored-By: Kate Gregory <4205167+KateGregory@users.noreply.github.com>

Author: claremacrae

_config.yml

@@ -83,8 +83,6 @@ yandex_site_verification :
 naver_site_verification  :
 
 # Social Sharing
-twitter:
-  username               : include_cpp
 facebook:
   username               :
   app_id                 :

_data/navigation.yml

@@ -1,7 +1,5 @@
 # main links
 main:
-  - title: "Twitter"
-    url: https://twitter.com/include_cpp
   - title: "Discord"
     url: /discord/
   # - title: "About"

index.md

@@ -58,7 +58,7 @@ Yes. See our <a class="page-link" href="/shop/">Shop</a> page. We have more than
 
 If you have joined our Discord, you can post in #meta-discord or DM an admin or moderator. Their names are highlighted in red or blue.
 
-You can also reach us either through [Twitter](https://twitter.com/include_cpp), or through the contact form below.
+You can also reach us through the contact form below.
 
 <form action="https://getsimpleform.com/messages?form_api_token=0249c3a7836e7b2532d7d6fe74e61676" method="post">
 <fieldset>

what-can-i-do.md

@@ -11,7 +11,6 @@ Everyone can help make the C++ community more welcoming and inclusive. May we su
 * Support our [conference scholarships](/conferences/scholarships/).
 * Adopt a [code of conduct](/resources/#conferences-and-codes-of-conduct) at things you run.
 * Encourage things you don't run (eg conferences that want you to attend or speak) to adopt a [code of conduct](/resources/#conferences-and-codes-of-conduct) and enforce it.
-* Follow us on [Twitter](https://twitter.com/include_cpp).
 * Let others know about us.
 * If you run a community resource or conference, you could add a link to this site, and ask us to add you to the [Community sponsors](/community-sponsors) page.