Revert "Create temp index on concept_counts during etl"

This reverts commit 46ccbce97d92764cbd6fe61079d76d516785579f.

This was missing an owner assignment and doesn't seem like a good
strategy. Better to keep the index and not to recreate it on every ETL
run.
Replace idx created/dropped on ETL w/ permanent

The ETL procedure i2b2_create_concept_counts() used to create and then
drop and index on concept_counts on the columns concept_path,
patient_count to speed up the query afterwards. I split the index into a
permanent single-column index on concept_path and a partial
single-column index on the patient_count index (only where the count is
0 because that's what the query cares about).