Update delivery time filter check for gridpool streams

Uses the new `is_valid` check that now comes with the delivery time filter.
This also drops the check that delivery start time  of the filter has to
be in the future, which is not desired for the gridpool data streaming
endpoints.

Signed-off-by: cwasicki <126617870+cwasicki@users.noreply.github.com>

Author: cwasicki

src/frequenz/client/electricity_trading/_client.py

@@ -300,8 +300,10 @@ def gridpool_orders_stream(
 
         Raises:
             grpc.RpcError: If an error occurs while streaming the orders.
+            ValueError: If an invalid delivery_time_filter is provided.
         """
-        self.validate_params(delivery_time_filter=delivery_time_filter)
+        if delivery_time_filter and not delivery_time_filter.is_valid:
+            raise ValueError("Invalid delivery_time_filter provided.")
 
         gridpool_order_filter = GridpoolOrderFilter(
             order_states=order_states,
@@ -366,8 +368,10 @@ def gridpool_trades_stream(
 
         Raises:
             grpc.RpcError: If an error occurs while streaming gridpool trades.
+            ValueError: If an invalid delivery_time_filter is provided.
         """
-        self.validate_params(delivery_time_filter=delivery_time_filter)
+        if delivery_time_filter and not delivery_time_filter.is_valid:
+            raise ValueError("Invalid delivery_time_filter provided.")
 
         gridpool_trade_filter = GridpoolTradeFilter(
             trade_states=trade_states,