test: Get rid of default wallet hacks

- Get rid of hardcoded wallet "" names and -wallet="" args
- Get rid of setup_nodes (-wallet, -nowallet, -disablewallet) argument rewriting

Motivation:

- Simplify test framework behavior so it's easier to write new tests without
  having arguments mangled by the framework
- Make tests more readable, replacing unexplained "" string literals with
  default_wallet_name references
- Make it trivial to update default wallet name and wallet data filename for
  sqlite #19077 testing
- Stop relying on -wallet arguments to create wallets, so it is easy to change
  -wallet option in the future to only load existing wallets not create new
  ones (to avoid accidental wallet creation, and encourage use of wallet
  encryption and descriptor features)

test/functional/wallet_import_rescan.py

@@ -151,7 +151,7 @@ class ImportRescanTest(BitcoinTestFramework):
         self.skip_if_no_wallet()
 
     def setup_network(self):
-        self.extra_args = [["-wallet="] for _ in range(self.num_nodes)]
+        self.extra_args = [[] for _ in range(self.num_nodes)]
         for i, import_node in enumerate(IMPORT_NODES, 2):
             if import_node.prune:
                 self.extra_args[i] += ["-prune=1"]
@@ -159,9 +159,8 @@ class ImportRescanTest(BitcoinTestFramework):
         self.add_nodes(self.num_nodes, extra_args=self.extra_args)
 
         # Import keys with pruning disabled
-        self.start_nodes(extra_args=[["-wallet="]] * self.num_nodes)
-        for n in self.nodes:
-            n.importprivkey(privkey=n.get_deterministic_priv_key().key, label='coinbase')
+        self.start_nodes(extra_args=[[]] * self.num_nodes)
+        self.import_deterministic_coinbase_privkeys()
         self.stop_nodes()
 
         self.start_nodes()