python 3.10: fix some deprecation warnings and compat with 3.10

electrum/sql_db.py

@@ -14,7 +14,7 @@ def sql(func):
     returns an awaitable asyncio.Future
     """
     def wrapper(self: 'SqlDB', *args, **kwargs):
-        assert threading.currentThread() != self.sql_thread
+        assert threading.current_thread() != self.sql_thread
         f = self.asyncio_loop.create_future()
         self.db_requests.put((f, func, args, kwargs))
         return f