[docs] remove blog article about searx-admin

- https://github.com/kvch/searx-admin last maintained 4 years ago
- searx-admin does not support 'use_default_settings' [1] (b4b81a5e)

[1] https://searxng.github.io/searxng/admin/settings.html#use-default-settings

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/blog/index.rst

@@ -8,7 +8,6 @@ Blog
 
    lxcdev-202006
    python3
-   admin
    intro-offline
    private-engines
    command-line-engines