Use direct references for some configuration variables (#10798)

Instead of proxying through the magic getter of the RootConfig
object. This should be more performant (and is more explicit).

synapse/handlers/identity.py

@@ -540,13 +540,13 @@ class IdentityHandler(BaseHandler):
 
         # It is already checked that public_baseurl is configured since this code
         # should only be used if account_threepid_delegate_msisdn is true.
-        assert self.hs.config.public_baseurl
+        assert self.hs.config.server.public_baseurl
 
         # we need to tell the client to send the token back to us, since it doesn't
         # otherwise know where to send it, so add submit_url response parameter
         # (see also MSC2078)
         data["submit_url"] = (
-            self.hs.config.public_baseurl
+            self.hs.config.server.public_baseurl
             + "_matrix/client/unstable/add_threepid/msisdn/submit_token"
         )
         return data