Drop the influx clients nothing ever held

`__slots__` and `__init__` carried `_write_client` and `_query_client` as
lazy state no method read.

backend/fluksio/flow/nodes/influx.py

@@ -174,8 +174,6 @@ class InfluxDbNode(Node):
         "timeout",
         "writes",
         "queries",
-        "_write_client",
-        "_query_client",
     )
 
     class Params(BaseModel):
@@ -231,10 +229,6 @@ class InfluxDbNode(Node):
         self.writes = cfg.writes
         self.queries = cfg.queries
 
-        # Lazy-initialized clients
-        self._write_client = None
-        self._query_client = None
-
         # Set default name
         if name is None:
             name = f"influxdb_{self.bucket}"