[mod] remove unused filter searx.webapp.extract_domain

it was used in the pix-art theme

searx/webapp.py

@@ -17,10 +17,7 @@ from html import escape
 from io import StringIO
 
 import urllib
-from urllib.parse import (
-    urlencode,
-    urlparse,
-)
+from urllib.parse import urlencode
 
 import httpx
 
@@ -349,12 +346,6 @@ def code_highlighter(codelines, language=None):
     return html_code
 
 
-# Extract domain from url
-@app.template_filter('extract_domain')
-def extract_domain(url):
-    return urlparse(url)[1]
-
-
 def get_current_theme_name(override=None):
     """Returns theme name.