test: Use MiniWallet in rpc_rawtransaction.py

This test was previously run twice, once with `--legacy-wallet` and once with
`--descriptors`.
Now we run it only with `--legacy-wallet`, as all the tests has been
ported to the MiniWallet but `raw_multisig_transaction_legacy_tests`,
which can be run only with the legacy wallet.
We also decrease the number of nodes used from 4 to 3, making the test
run slightly faster.

test/functional/test_runner.py

@@ -183,7 +183,6 @@ BASE_SCRIPTS = [
     'rpc_signrawtransaction.py --legacy-wallet',
     'rpc_signrawtransaction.py --descriptors',
     'rpc_rawtransaction.py --legacy-wallet',
-    'rpc_rawtransaction.py --descriptors',
     'wallet_groups.py --legacy-wallet',
     'wallet_transactiontime_rescan.py --descriptors',
     'wallet_transactiontime_rescan.py --legacy-wallet',