Remove unused vector

src/google/protobuf/compiler/parser.cc

@@ -525,7 +525,6 @@ bool Parser::Parse(io::Tokenizer* input, FileDescriptorProto* file) {
   SourceCodeInfo source_code_info;
   source_code_info_ = &source_code_info;
 
-  vector<string> top_doc_comments;
   if (LookingAtType(io::Tokenizer::TYPE_START)) {
     // Advance to first token.
     input_->NextWithComments(NULL, &upcoming_detached_comments_,