submarine swaps: remove support for 'old' normal swaps,

where the user has the preimage.

The CLTV requirements between old and new flow are imcompatible.
With the current locktime value, the server was vulnerable to an
attack where the client does not settle the lightning payment
and claims a refund. In order to support both old and new flows,
one would need to use different locktimes.

electrum/plugins/swapserver/server.py

@@ -105,7 +105,6 @@ class SwapServer(Logger, EventListener):
         their_pubkey = bytes.fromhex(request['refundPublicKey'])
         assert len(their_pubkey) == 33
         swap = self.sm.create_reverse_swap(
-            payment_hash=None,
             lightning_amount_sat=lightning_amount_sat,
             their_pubkey=their_pubkey
         )
@@ -121,6 +120,8 @@ class SwapServer(Logger, EventListener):
         return web.json_response(response)
 
     async def create_swap(self, r):
+        # reverse for client, forward for server
+        # requesting a normal swap (old protocol) will raise an exception
         self.sm.init_pairs()
         request = await r.json()
         req_type = request['type']
@@ -145,28 +146,6 @@ class SwapServer(Logger, EventListener):
                 'timeoutBlockHeight': swap.locktime,
                 "onchainAmount": swap.onchain_amount,
             }
-        elif req_type == 'submarine':
-            # old protocol
-            their_invoice=request['invoice']
-            their_pubkey=bytes.fromhex(request['refundPublicKey'])
-            assert len(their_pubkey) == 33
-            lnaddr = lndecode(their_invoice)
-            payment_hash = lnaddr.paymenthash
-            lightning_amount_sat = int(lnaddr.get_amount_sat()) # should return int
-            swap = self.sm.create_reverse_swap(
-                lightning_amount_sat=lightning_amount_sat,
-                payment_hash=payment_hash,
-                their_pubkey=their_pubkey
-            )
-            self.sm.add_invoice(their_invoice, pay_now=False)
-            response = {
-                "id": payment_hash.hex(),
-                "acceptZeroConf": False,
-                "expectedAmount": swap.onchain_amount,
-                "timeoutBlockHeight": swap.locktime,
-                "address": swap.lockup_address,
-                "redeemScript": swap.redeem_script.hex()
-            }
         else:
             raise Exception('unsupported request type:' + req_type)
         return web.json_response(response)