hardware wallets: wizard no longer requests xpub at path "m"

This was done to calculate the bip32 root fingerprint but it broke
the digitalbitbox. The keystore already had a different way to get
the root fingerprint for existing wallets, specifically handling this
case; the code in base_wizard used when creating new wallets was
duplicating that code originally and was then forgotten to be updated.
Now these codepaths are unified.

closes #5816

electrum/plugins/hw_wallet/plugin.py

@@ -175,6 +175,13 @@ class HardwareClientBase:
     def get_xpub(self, bip32_path: str, xtype) -> str:
         raise NotImplementedError()
 
+    def request_root_fingerprint_from_device(self) -> str:
+        # digitalbitbox (at least) does not reveal xpubs corresponding to unhardened paths
+        # so ask for a direct child, and read out fingerprint from that:
+        child_of_root_xpub = self.get_xpub("m/0'", xtype='standard')
+        root_fingerprint = BIP32Node.from_xkey(child_of_root_xpub).fingerprint.hex().lower()
+        return root_fingerprint
+
 
 def is_any_tx_output_on_change_branch(tx: PartialTransaction) -> bool:
     return any([txout.is_change for txout in tx.outputs()])