Make try_get_string_data_array a non-member function

It doesn't need to be. It's truly static.
We want to be able to call it from local static functions.

Author: Joel Allred

src/util/simplify_expr.cpp

@@ -63,6 +63,11 @@ struct simplify_expr_cachet
 simplify_expr_cachet simplify_expr_cache;
 #endif
 
+static optionalt<std::reference_wrapper<const array_exprt>>
+try_get_string_data_array(
+  const refined_string_exprt &s,
+  const namespacet &ns);
+
 simplify_exprt::resultt<> simplify_exprt::simplify_abs(const abs_exprt &expr)
 {
   if(expr.op().is_constant())
@@ -1818,8 +1823,20 @@ optionalt<std::string> simplify_exprt::expr2bits(
   return {};
 }
 
-optionalt<std::reference_wrapper<const array_exprt>>
-  simplify_exprt::try_get_string_data_array(
+/// Get char sequence from refined string expression
+///
+/// If `s.content()` is of the form `&id[e]`, where `id` is an array-typed
+/// symbol expression (and `e` is any expression), return the value of the
+/// symbol `id` (as given by the `value` field of the symbol in the namespace
+/// `ns`); otherwise return an empty optional.
+///
+/// \param s: refined string expression
+/// \param ns: namespace
+/// \return array expression representing the char sequence which forms the
+///   content of the refined string expression, empty optional if the content
+///   cannot be determined
+static optionalt<std::reference_wrapper<const array_exprt>>
+  try_get_string_data_array(
     const refined_string_exprt &s,
     const namespacet &ns)
 {

src/util/simplify_expr_class.h

@@ -221,22 +221,6 @@ class simplify_exprt
   replace_mapt local_replace_map;
 #endif
 
-  /// Get char sequence from refined string expression
-  ///
-  /// If `s.content()` is of the form `&id[e]`, where `id` is an array-typed
-  /// symbol expression (and `e` is any expression), return the value of the
-  /// symbol `id` (as given by the `value` field of the symbol in the namespace
-  /// `ns`); otherwise return an empty optional.
-  ///
-  /// \param s: refined string expression
-  /// \param ns: namespace
-  /// \return array expression representing the char sequence which forms the
-  ///   content of the refined string expression, empty optional if the content
-  ///   cannot be determined
-  static optionalt<std::reference_wrapper<const array_exprt>>
-    try_get_string_data_array(
-      const refined_string_exprt &s,
-      const namespacet &ns);
 };
 
 #endif // CPROVER_UTIL_SIMPLIFY_EXPR_CLASS_H