mark RelayableRetraction and SignedRetraction as deprecated

The normal Rectraction can be used for this:

* RelayableRetraction: Both the author and the parent author can retract
  a relayable, so there is no need to check if it was relayed.
* SignedRetraction: this is already signed at the salmon-level. No need
  to add an additional signature at this level. Only used for
  StatusMessage.

lib/diaspora_federation/entities/relayable_retraction.rb

@@ -17,6 +17,7 @@ module DiasporaFederation
     # is not checked, only parent_author_signature is checked.
     #
     # @see Validators::RelayableRetractionValidator
+    # @deprecated will be replaced with {Entities::Retraction}
     class RelayableRetraction < Entity
       # @!attribute [r] parent_author_signature
       #   Contains a signature of the entity using the private key of the author of a parent post

lib/diaspora_federation/entities/signed_retraction.rb

@@ -4,6 +4,7 @@ module DiasporaFederation
     # entity of post type ({Entities::StatusMessage})
     #
     # @see Validators::SignedRetractionValidator
+    # @deprecated will be replaced with {Entities::Retraction}
     class SignedRetraction < Entity
       # @!attribute [r] target_guid
       #   guid of a post to be deleted

lib/diaspora_federation/validators/relayable_retraction_validator.rb

@@ -1,6 +1,7 @@
 module DiasporaFederation
   module Validators
     # This validates a {Entities::RelayableRetraction}
+    # @deprecated the {Entities::RelayableRetraction} will be replaced with {Entities::Retraction}
     class RelayableRetractionValidator < Validation::Validator
       include Validation
 

lib/diaspora_federation/validators/signed_retraction_validator.rb

@@ -1,6 +1,7 @@
 module DiasporaFederation
   module Validators
     # This validates a {Entities::SignedRetraction}
+    # @deprecated the {Entities::RelayableRetraction} will be replaced with {Entities::Retraction}
     class SignedRetractionValidator < Validation::Validator
       include Validation