Remove default values for partition_id

Problem

We added a default value for partition_id to several CI models in order to populate the data quickly and backfill incorrect values with a migration.

Solution

We need to remove this constraint for the following models, similar to what we did in !141071 (merged).

• Ci::DailyBuildGroupReportResult, !155046 (merged)
• Ci::PipelineMessage, !155397 (merged)
• Ci::SourceProject, !157909 (merged)

cc @tianwenchen