delete declaration for jsonnet_unparse_jsonnet (which doesn't exist)

Reported in #1012

Author: johnbartholomew

core/parser.h

@@ -38,11 +38,6 @@ AST *jsonnet_parse(Allocator *alloc, Tokens &tokens);
  */
 std::string jsonnet_unparse_number(double v);
 
-/** The inverse of jsonnet_parse.
- */
-std::string jsonnet_unparse_jsonnet(const AST *ast, const Fodder &final_fodder, unsigned indent,
-                                    bool pad_arrays, bool pad_objects, char comment_style);
-
 }  // namespace jsonnet::internal
 
 #endif  // JSONNET_PARSER_H