Delete ldap group links upon group deletion

app/models/group.rb

@@ -21,7 +21,7 @@ class Group < Namespace
   has_many :users, through: :users_groups
   has_many :project_group_links, dependent: :destroy
   has_many :shared_projects, through: :project_group_links, source: :project
-  has_many :ldap_group_links, foreign_key: 'group_id'
+  has_many :ldap_group_links, foreign_key: 'group_id', dependent: :destroy
 
   validate :avatar_type, if: ->(user) { user.avatar_changed? }
   validates :avatar, file_size: { maximum: 100.kilobytes.to_i }