api: kind of fix for the SWHRemoteAPI's contructor

- ensure we do accept **kwargs so any super().__init__(**kwargs) from an
  unexpected MRO path in an indecent maze of multi-inheritance will not crash
- do not call super().__init__(); it is either useless (most probably,
  super() is object in this context) or silently ignore passed kwargs that
  super() (when it's not object) may have been able to understand...

Long story short, kwargs handling in multi-inheritance __init__ methods is
a mess.

swh/core/api/__init__.py

@@ -141,8 +141,8 @@ class SWHRemoteAPI(metaclass=MetaSWHRemoteAPI):
     This backend class will never be instantiated, it only serves as
     a template."""
 
-    def __init__(self, api_exception, url, timeout=None, chunk_size=4096):
-        super().__init__()
+    def __init__(self, api_exception, url,
+                 timeout=None, chunk_size=4096, **kwargs):
         self.api_exception = api_exception
         base_url = url if url.endswith('/') else url + '/'
         self.url = base_url