Allow project to be set up to push to and pull from same mirror

changelogs/unreleased-ee/dm-remote-mirror-url-availability.yml

+---
+title: Allow project to be set up to push to and pull from same mirror
+merge_request:
+author:
+type: fixed

ee/app/models/ee/project.rb

@@ -334,12 +334,6 @@ module EE
       repository.async_remove_remote(::Repository::MIRROR_REMOTE)
     end
 
-    def import_url_availability
-      if remote_mirrors.find_by(url: import_url)
-        errors.add(:import_url, 'is already in use by a remote mirror')
-      end
-    end
-
     def username_only_import_url
       bare_url = read_attribute(:import_url)
       return bare_url unless ::Gitlab::UrlSanitizer.valid?(bare_url)

ee/app/models/remote_mirror.rb

@@ -17,8 +17,6 @@ class RemoteMirror < ActiveRecord::Base
   belongs_to :project, inverse_of: :remote_mirrors
 
   validates :url, presence: true, url: { protocols: %w(ssh git http https), allow_blank: true }
-
-  validate  :url_availability, if: -> (mirror) { mirror.url_changed? || mirror.enabled? }
   validates :url, addressable_url: true, if: :url_changed?
 
   before_save :set_new_remote_name, if: :mirror_url_changed?
@@ -174,14 +172,6 @@ class RemoteMirror < ActiveRecord::Base
     end
   end
 
-  def url_availability
-    return unless project
-
-    if project.import_url == url && project.mirror?
-      errors.add(:url, 'is already in use')
-    end
-  end
-
   def reset_fields
     update_columns(
       last_error: nil,