Bug 1221064 - improve job list performance

The job list endpoint was joining the job table and the resultset table
with the only purpose of sorting the results by push_timestamp.Also we
don't really need any sorting on that endpoint, so let's remove it.

tests/webapp/api/test_jobs_api.py

@@ -60,11 +60,6 @@ def test_job_list(webapp, eleven_jobs_stored, jm):
     for job in jobs:
         assert set(job.keys()) == set(exp_keys)
 
-    # The jobs should be returned in order of descending order
-    # of their resultset's push_timestamp, so in this case the
-    # first job should have id of 10.
-    assert jobs[0]['id'] == 10
-
 
 def test_job_list_bad_project(webapp, eleven_jobs_stored, jm):
     """

treeherder/model/sql/jobs.json

@@ -482,15 +482,11 @@
                     ON j.`job_type_id` = jt.id
 				  LEFT JOIN `REP0`.`job_group` as jg
                     ON jt.`job_group_id` = jg.id
-                  LEFT JOIN result_set rs
-                    ON rs.id = j.result_set_id
                   LEFT JOIN `REP0`.reference_data_signatures rds
                     ON j.signature = rds.signature
                   WHERE 1
                   REP1
                   GROUP BY j.id
-                  ORDER BY
-                    rs.push_timestamp DESC
                   ",
 
             "host_type":"read_host"