cgit: rewrite the CGit lister

Simplify the code:
- do only inherit from ListerBase
- implement HTTP queries directly using requests
- get rid of convoluted code

Make the origin_url gathered from the git repo's "project" page instead of
building it from the 'url_prefix' hack. Now, the lister WILL make substancially
more requests, since it will make one request per listed git repo, but
the provided origin_url should be pretty reliable now.

When several url are provided as clonable URLs, choose the http/https one first,
otherwise, choose the first one of the list.

Add proper tests for the cgit lister.

Also, get rid of the 'time_updated' column in the model.

swh/lister/tests/test_cli.py

@@ -61,7 +61,6 @@ def test_get_lister_override():
     listers = {
         'gitlab': ('api_baseurl', 'https://gitlab.uni/api/v4/'),
         'phabricator': ('forge_url', 'https://somewhere.org'),
-        'cgit': ('url_prefix', 'https://some-cgit.eu/'),
     }
 
     # check the override ends up defined in the lister
@@ -87,8 +86,6 @@ def test_get_lister_override():
 
         # then the default base url is used
         default_url = DEFAULT_BASEURLS[lister_name]
-        if isinstance(default_url, tuple):  # cgit implementation detail...
-            default_url = default_url[1]
 
         assert getattr(lst, url_key) == default_url
         assert 'priority' not in lst.config