wallet db upgrade: rm support of "legacy" lightning channels

("legacy" as in pre-static-remote-key channels)

electrum/wallet_db.py

@@ -52,7 +52,7 @@ if TYPE_CHECKING:
 
 OLD_SEED_VERSION = 4        # electrum versions < 2.0
 NEW_SEED_VERSION = 11       # electrum versions >= 2.0
-FINAL_SEED_VERSION = 48     # electrum >= 2.7 will set this to prevent
+FINAL_SEED_VERSION = 49     # electrum >= 2.7 will set this to prevent
                             # old versions from overwriting new format
 
 
@@ -197,6 +197,7 @@ class WalletDB(JsonDB):
         self._convert_version_46()
         self._convert_version_47()
         self._convert_version_48()
+        self._convert_version_49()
         self.put('seed_version', FINAL_SEED_VERSION)  # just to be sure
 
         self._after_upgrade_tasks()
@@ -953,6 +954,22 @@ class WalletDB(JsonDB):
                 item['amount_msat'] = "!"
         self.data['seed_version'] = 48
 
+    def _convert_version_49(self):
+        if not self._is_upgrade_method_needed(48, 48):
+            return
+        channels = self.data.get('channels', {})
+        legacy_chans = [chan_dict for chan_dict in channels.values()
+                        if chan_dict['channel_type'] == ChannelType.OPTION_LEGACY_CHANNEL]
+        if legacy_chans:
+            raise WalletFileException(
+                f"This wallet contains {len(legacy_chans)} lightning channels of type 'LEGACY'. "
+                f"These channels were created using unreleased development versions of Electrum "
+                f"before the first lightning-capable release of 4.0, and are not supported anymore. "
+                f"Please use Electrum 4.3.0 to open this wallet, close the channels, "
+                f"and delete them from the wallet."
+            )
+        self.data['seed_version'] = 49
+
     def _convert_imported(self):
         if not self._is_upgrade_method_needed(0, 13):
             return