refactor: rename rpc_getorphantxs to rpc_orphans

Generalizes the test to accommodate additional
orphan-related RPCs

test/functional/test_runner.py

@@ -160,7 +160,7 @@ BASE_SCRIPTS = [
     'wallet_importmulti.py --legacy-wallet',
     'mempool_limit.py',
     'rpc_txoutproof.py',
-    'rpc_getorphantxs.py',
+    'rpc_orphans.py',
     'wallet_listreceivedby.py --legacy-wallet',
     'wallet_listreceivedby.py --descriptors',
     'wallet_abandonconflict.py --legacy-wallet',