remove refined_string_exprt constructor

This has no users.

Author: Daniel Kroening

src/util/string_expr.h

@@ -108,15 +108,6 @@ inline const array_string_exprt &to_array_string_expr(const exprt &expr)
 class refined_string_exprt : public struct_exprt
 {
 public:
-  DEPRECATED(SINCE(
-    2019,
-    1,
-    12,
-    "use refined_string_exprt(length, content, type) instead"))
-  refined_string_exprt() : struct_exprt()
-  {
-  }
-
   refined_string_exprt(
     const exprt &_length,
     const exprt &_content,