Remove the Jobs table

This table has been superfluous for a long time.

src/sql/upgrade-67.sql

@@ -0,0 +1,4 @@
+alter table Builds drop constraint builds_project_fkey2;
+alter table BuildMetrics drop constraint buildmetrics_project_fkey2;
+alter table StarredJobs drop constraint starredjobs_project_fkey2;
+drop table Jobs;