Remove the backend changes for automatic diff summary

.rubocop_todo/rspec/before_all_role_assignment.yml

.rubocop_todo/rspec/named_subject.yml

.rubocop_todo/style/inline_disable_annotation.yml

doc/api/graphql/reference/index.md

...cripts/merge_requests/queries/summary_notes.query.graphql

ee/app/graphql/ee/types/merge_request_type.rb

ee/app/graphql/types/merge_request_diff_type.rb

ee/app/graphql/types/merge_requests/diff_llm_summary_type.rb

ee/app/helpers/ee/merge_requests_helper.rb

ee/app/helpers/ee/todos_helper.rb

ee/app/models/ee/merge_request.rb

ee/app/models/ee/merge_request_diff.rb

ee/app/models/merge_request/diff_llm_summary.rb

ee/app/policies/ee/merge_request_policy.rb

ee/app/policies/merge_request/diff_llm_summary_policy.rb

ee/app/services/ee/notification_service.rb

ee/app/services/llm/merge_requests/summarize_diff_service.rb

ee/app/services/llm/summarize_merge_request_service.rb

ee/app/views/notify/_diff_summary.html.haml

ee/app/views/notify/_diff_summary.text.erb