User is not automatically removed from suggested approvers list if user is deleted.

CHANGELOG-EE

 v 8.4.0 (unreleased)
   - Add ability to create a note for user by admin
   - Fix "Commit was rejected by git hook", when max_file_size was set null in project's Git hooks
+  - Fix "User is not automatically removed from suggested approvers list if user is deleted"
 
 v 8.3.2
   - No EE-specific changes

app/models/user.rb

@@ -137,6 +137,7 @@ class User < ActiveRecord::Base
   has_many :assigned_merge_requests,  dependent: :destroy, foreign_key: :assignee_id, class_name: "MergeRequest"
   has_many :oauth_applications,       class_name: 'Doorkeeper::Application', as: :owner, dependent: :destroy
   has_many :approvals,                dependent: :destroy
+  has_many :approvers,                dependent: :destroy
   has_one  :abuse_report,             dependent: :destroy
   has_many :builds,                   dependent: :nullify, class_name: 'Ci::Build'