builds: drop project, jobset columns

Indexes were haphazardly dropped.

src/sql/upgrade-80.sql

@@ -0,0 +1,9 @@
+drop index IndexBuildsOnJobsetIsCurrent;
+drop index IndexBuildsOnJobIsCurrent;
+drop index IndexBuildsOnJobset;
+drop index IndexBuildsOnProject;
+drop index IndexBuildsOnJobFinishedId;
+
+alter table Builds
+    drop column project,
+    drop column jobset;