Update Open Graph logic and remove unused OGP image

Removed the fallback Open Graph image logic from the header and deleted the unused `ogp.png` file. Also removed the `image` field from `_config.yml` as it is no longer necessary. Simplifies configuration and ensures only page-specific images are used.

_config.yml

@@ -3,7 +3,6 @@ description: >-
   Some dude in the internet.
 lang: en-US
 timezone: Europe/Berlin
-image: assets/img/ogp.png
 mode: dark # default theme "dark" | "light"
 
 # Profile settings

_includes/header.html

@@ -96,8 +96,6 @@
   />
   {% if page.image %}
   <meta property="og:image" content="{{ page.image | absolute_url }}" />
-  {% else %}
-  <meta property="og:image" content="{{ site.image | absolute_url }}" />
   {% endif %}
   <meta property="og:image:width" content="640" />
   <meta property="og:image:height" content="640" />