Merge branch '29976-fix-dropping-job_id' into 'master'

Do try to drop it if ci_builds.job_id isn't there

Closes #29976

See merge request !10216

db/migrate/20170301205639_remove_unused_ci_tables_and_columns.rb

@@ -17,7 +17,7 @@ class RemoveUnusedCiTablesAndColumns < ActiveRecord::Migration
     end
     remove_column :ci_pipelines, :push_data, :text
-    remove_column :ci_builds, :job_id, :integer
+    remove_column :ci_builds, :job_id, :integer if column_exists?(:ci_builds, :job_id)
     remove_column :ci_builds, :deploy, :boolean
   end