[tests] Remove rpc_zmq.py

rpc_zmq.py is racy and fails intermittently. Remove that test file and
move the getzmqnotifications RPC test into interface_zmq.py

test/functional/test_runner.py

@@ -152,7 +152,6 @@ BASE_SCRIPTS = [
     'feature_versionbits_warning.py',
     'rpc_preciousblock.py',
     'wallet_importprunedfunds.py',
-    'rpc_zmq.py',
     'rpc_signmessage.py',
     'feature_nulldummy.py',
     'mempool_accept.py',