regtests: test_watchtower started failing due to newly exposed bug

local_watchtower.adb.start_network was getting called twice.

follow-up 6ac3f84095

```
20230418T014725.636141Z |    ERROR | __main__ |
Traceback (most recent call last):
  File "/home/user/wspace/electrum/./run_electrum", line 435, in main
    handle_cmd(
  File "/home/user/wspace/electrum/./run_electrum", line 469, in handle_cmd
    d = daemon.Daemon(config, fd)
  File "/home/user/wspace/electrum/electrum/util.py", line 462, in <lambda>
    return lambda *args, **kw_args: do_profile(args, kw_args)
  File "/home/user/wspace/electrum/electrum/util.py", line 458, in do_profile
    o = func(*args, **kw_args)
  File "/home/user/wspace/electrum/electrum/daemon.py", line 404, in __init__
    self.network = Network(config, daemon=self)
  File "/home/user/wspace/electrum/electrum/network.py", line 348, in __init__
    self.local_watchtower.adb.start_network(self)
  File "/home/user/wspace/electrum/electrum/address_synchronizer.py", line 185, in start_network
    assert self.network is None, "already started"
AssertionError: already started
```

electrum/lnwatcher.py

@@ -324,7 +324,7 @@ class WatchTower(LNWatcher):
 
     LOGGING_SHORTCUT = 'W'
 
-    def __init__(self, network):
+    def __init__(self, network: 'Network'):
         adb = AddressSynchronizer(WalletDB({}, manual_upgrades=False), network.config, name=self.diagnostic_name())
         adb.start_network(network)
         LNWatcher.__init__(self, adb, network)

electrum/network.py

@@ -345,7 +345,6 @@ class Network(Logger, NetworkRetryManager[ServerAddr]):
         if self.config.get('run_watchtower', False):
             from . import lnwatcher
             self.local_watchtower = lnwatcher.WatchTower(self)
-            self.local_watchtower.adb.start_network(self)
             asyncio.ensure_future(self.local_watchtower.start_watching())
 
     def has_internet_connection(self) -> bool: