api: remove 'addr' param from message dispatcher

Now that jsoncomm is using a connection oriented protocol, the
`addr` parameter is not needed[*] and can thus be removed from
the `BaseAPI._message` message dispatcher. Adapt all usages
of it, including the tests.

[*] sendmsg ignores the destination parameter for connection
oriented sockets.

test/mod/test_api.py

@@ -23,12 +23,12 @@ class APITester(osbuild.api.BaseAPI):
 
     endpoint = "test-api"
 
-    def _message(self, msg, _fds, sock, addr):
+    def _message(self, msg, _fds, sock):
         self.messages += 1
 
         if msg["method"] == "echo":
             msg["method"] = "reply"
-            sock.send(msg, destination=addr)
+            sock.send(msg)
 
     def _cleanup(self):
         self.clean = True