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/mempool_compatibility.py

@@ -21,6 +21,7 @@ from test_framework.test_framework import BitcoinTestFramework
 class MempoolCompatibilityTest(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 2
+        self.wallet_names = [None, self.default_wallet_name]
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()
@@ -31,7 +32,7 @@ class MempoolCompatibilityTest(BitcoinTestFramework):
             150200, # oldest version supported by the test framework
             None,
         ])
-        self.start_nodes([[], ["-wallet="]])
+        self.start_nodes()
         self.import_deterministic_coinbase_privkeys()
 
     def run_test(self):