Make logo CDN domain into simple config

Having this as a function which does string parsing and manipulation
surprised me a bit when I was trying to figure out why something wasn’t
working.

It’s more in line with the way we do other config like this (for example
`ASSET_PATH`) to make it a simple config variable, rather than trying to
be clever and guess things based on other config variables.

It’s also less code, and is explicit enough that it doesn’t need tests.

app/utils/__init__.py

@@ -1,8 +1,7 @@
 from functools import wraps
 from itertools import chain
-from urllib.parse import urlparse
 
-from flask import abort, current_app, g, make_response, request
+from flask import abort, g, make_response, request
 from flask_login import current_user
 from notifications_utils.field import Field
 from orderedset._orderedset import OrderedSet
@@ -36,18 +35,6 @@ def get_help_argument():
     return request.args.get('help') if request.args.get('help') in ('1', '2', '3') else None
 
 
-def get_logo_cdn_domain():
-    parsed_uri = urlparse(current_app.config['ADMIN_BASE_URL'])
-
-    if parsed_uri.netloc.startswith('localhost'):
-        return 'static-logos.notify.tools'
-
-    subdomain = parsed_uri.hostname.split('.')[0]
-    domain = parsed_uri.netloc[len(subdomain + '.'):]
-
-    return "static-logos.{}".format(domain)
-
-
 def parse_filter_args(filter_dict):
     if not isinstance(filter_dict, MultiDict):
         filter_dict = MultiDict(filter_dict)