[Python] Avoid session configuration in data generator

[tonyyang-svail]

The session configuration is only used for Hive, so it shouldn't be part of the data generator API.

The driver name and the session info can be stored at the connection struct so that we can avoid passing them to data generator.

sqlflow/sql/python/sqlflow_submitter/db.py

Lines 47 to 49 in 5653d09

	def db_generator(driver, conn, session_cfg, statement,
	feature_column_names, label_column_name,
	feature_specs, fetch_size=128):