Use delete_all for deleting events

Because we don't have any destroy callbacks (or other logic
triggered on event destroy), there is no reason for deleting events
inefficiently one by one, instead we can use :delete_all.

app/models/issue.rb

@@ -31,7 +31,7 @@ class Issue < ApplicationRecord
   has_internal_id :iid, scope: :project, init: ->(s) { s&.project&.issues&.maximum(:iid) }
-  has_many :events, as: :target, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+  has_many :events, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
   has_many :merge_requests_closing_issues,
     class_name: 'MergeRequestsClosingIssues',

app/models/merge_request.rb

@@ -54,7 +54,7 @@ class MergeRequest < ApplicationRecord
   belongs_to :head_pipeline, foreign_key: "head_pipeline_id", class_name: "Ci::Pipeline"
-  has_many :events, as: :target, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+  has_many :events, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
   has_many :merge_requests_closing_issues,
     class_name: 'MergeRequestsClosingIssues',

app/models/milestone.rb

@@ -37,7 +37,7 @@ class Milestone < ApplicationRecord
   has_many :issues
   has_many :labels, -> { distinct.reorder('labels.title') }, through: :issues
   has_many :merge_requests
-  has_many :events, as: :target, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+  has_many :events, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
   scope :of_projects, ->(ids) { where(project_id: ids) }
   scope :of_groups, ->(ids) { where(group_id: ids) }

app/models/note.rb

@@ -78,7 +78,7 @@ class Note < ApplicationRecord
   # suggestions.delete_all calls
   has_many :suggestions, -> { order(:relative_order) },
     inverse_of: :note, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
-  has_many :events, as: :target, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+  has_many :events, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
   has_one :system_note_metadata
   has_one :note_diff_file, inverse_of: :diff_note, foreign_key: :diff_note_id

app/models/user.rb

@@ -131,7 +131,7 @@ class User < ApplicationRecord
   has_many :notes,                    dependent: :destroy, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :issues,                   dependent: :destroy, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :merge_requests,           dependent: :destroy, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
-  has_many :events,                   dependent: :destroy, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
+  has_many :events,                   dependent: :delete_all, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :releases,                 dependent: :nullify, foreign_key: :author_id # rubocop:disable Cop/ActiveRecordDependent
   has_many :subscriptions,            dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
   has_many :oauth_applications, class_name: 'Doorkeeper::Application', as: :owner, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent

spec/models/user_spec.rb

@@ -32,7 +32,7 @@ describe User do
     it { is_expected.to have_many(:groups) }
     it { is_expected.to have_many(:keys).dependent(:destroy) }
     it { is_expected.to have_many(:deploy_keys).dependent(:nullify) }
-    it { is_expected.to have_many(:events).dependent(:destroy) }
+    it { is_expected.to have_many(:events).dependent(:delete_all) }
     it { is_expected.to have_many(:issues).dependent(:destroy) }
     it { is_expected.to have_many(:notes).dependent(:destroy) }
     it { is_expected.to have_many(:merge_requests).dependent(:destroy) }