Configuring UDFs via plugin variables looks not a good idea.
The more variables Spider has, the more complex it becomes.
Further, I expect that only a few users use Spider UDFs.

Deprecate the following plugin variables regarding Spider UDFs:

* spider_udf_ds_bulk_insert_rows
* spider_udf_ds_table_loop_mode
* spider_udf_ds_use_real_table
* spider_udf_ct_bulk_insert_interval
* spider_udf_ct_bulk_insert_rows

spider_udf_table_lock_mutex_count and spider_udf_table_mon_mutex_count
are also for tweaking UDFs but they are already read-only. So,
there is no need to deprecate them.