swaps: rm until filter when fetching server pairs

The `until` filter would limit the relay to only send us events created
up until this timestamp. If the user opens a swap transport by opening
the swap dialog, and keeps the dialog open the dialog will naturally age
above this limit and the relay will stop sending the client swapserver
events as they have (legitimately) been created after this timestamp.

As sanity check we still have the comparison against the current
timestamp in the event parsing loop to prevent pre/backdating.

Fixes https://github.com/spesmilo/electrum/issues/10520

electrum/submarine_swaps.py

@@ -1847,7 +1847,6 @@ class NostrTransport(SwapServerTransport):
             "#d": [f"electrum-swapserver-{self.NOSTR_EVENT_VERSION}"],
             "#r": [f"net:{constants.net.NET_NAME}"],
             "since": int(time.time()) - 60 * 60,
-            "until": int(time.time()) + 60 * 60,
         }
         async for event in self.relay_manager.get_events(query, single_event=False, only_stored=False):
             try: