Revert "db: since we select based on past scheduled unfinished items, this should also be indexed"
Revert "db: since we select based on past scheduled unfinished items, this should also be indexed"

This reverts commit 6a62485e4839614af965fc389b1461de6ccc8be8.

Causes follow up error

2019-08-08T17:53:29.555Z - debug: PostgreSQL._query('CREATE INDEX copy_paths_started_is_null_idx ON copy_paths (started IS NULL)',id='0573da'): "done (concurrent=1), (query_time_ms=31) -- error: Error: ERROR:  syntax error at or near \"IS\"\nLINE 1: ...py_paths_started_is_null_idx ON copy_paths (started IS NULL)\n                                                               ^\n"
2019-08-08T17:53:29.555Z - debug: PostgreSQL.update_schema: "error updating table schemas -- postgresql Error: ERROR:  syntax error at or near \"IS\"\nLINE 1: ...py_paths_started_is_null_idx ON copy_paths (started IS NULL)\n                                                               ^\n"
2019-08-08T17:53:29.556Z - error: Error starting hub services! err=postgresql Error: ERROR:  syntax error at or near "IS"
LINE 1: ...py_paths_started_is_null_idx ON copy_paths (started IS NULL)
                                                               ^

DrXyzzy/smc,tscholl2/smc,sagemathinc/smc,DrXyzzy/smc,DrXyzzy/smc,tscholl2/smc,DrXyzzy/smc,sagemathinc/smc,tscholl2/smc,tscholl2/smc,tscholl2/smc,sagemathinc/smc,sagemathinc/smc