Histories members -> poof!

We however have Histories in constructor, which we will remove out of the way
soon.

src/translator/response.cpp

@@ -10,7 +10,7 @@ namespace bergamot {
 
 Response::Response(AnnotatedText &&source, Histories &&histories,
                    std::vector<Ptr<Vocab const>> &vocabs)
-    : source(std::move(source)), histories_(std::move(histories)) {
+    : source(std::move(source)) {
   // Reserving length at least as much as source_ seems like a reasonable thing
   // to do to avoid reallocations.
   target.text.reserve(source.text.size());

src/translator/response.h

@@ -52,8 +52,7 @@ class Response {
   Response(Response &&other)
       : source(std::move(other.source)), target(std::move(other.target)),
         alignments(std::move(other.alignments)),
-        qualityScores(std::move(other.qualityScores)),
-        histories_(std::move(other.histories_)){};
+        qualityScores(std::move(other.qualityScores)){};
 
   // The following copy bans are not stricitly required anymore since Annotation
   // is composed of the ByteRange primitive (which was previously string_view
@@ -87,13 +86,6 @@ class Response {
   /// sparse matrix representation with indices corresponding
   /// to (sub-)words accessible through Annotation.
   std::vector<Alignment> alignments;
-
-  /// Access to histories, which holds rich information on translated text.
-  /// Not recommended to use, will be removed in future.
-  const Histories &histories() const { return histories_; }
-
-private:
-  Histories histories_;
 };
 } // namespace bergamot
 } // namespace marian