Delete state transitions with no state change

Migration to delete state transitions where same state present in both from_state and to_state

Migration and query analysis:

bundle exec rake db:migrate       
main: == 20221013215832 CleanupVulnerabilityStateTransitionsWithSameFromStateToState: migrating 
main: == 20221013215832 CleanupVulnerabilityStateTransitionsWithSameFromStateToState: migrated (0.0184s) 

ci: == 20221013215832 CleanupVulnerabilityStateTransitionsWithSameFromStateToState: migrating 
ci: -- The migration is skipped since it modifies the schemas: [:gitlab_main].
ci: -- This database can only apply migrations in one of the following schemas: [:gitlab_ci, :gitlab_shared, :gitlab_internal].
ci: == 20221013215832 CleanupVulnerabilityStateTransitionsWithSameFromStateToState: migrated (0.0003s) 

[ gprd ] production> Vulnerabilities::StateTransition.count
=> 1759754
[ gprd ] production>  Vulnerabilities::StateTransition.where('from_state = to_state').count
=> 178153
[ gstg ] production> Vulnerabilities::StateTransition.where('from_state = to_state').count
=> 0

DELETE from vulnerability_state_transitions where from_state = to_state;

Time: 2.867 s
  - planning: 0.696 ms
  - execution: 2.867 s
    - I/O read: 907.333 ms
    - I/O write: 0.000 ms

https://gitlab.slack.com/archives/CLJMDRD8C/p1665697592125439 https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/12629/commands/44571

Related to #376356 (closed)