Remove unnecessary const auto

Author: andrjohns

stan/math/rev/fun/inv_Phi.hpp

@@ -36,7 +36,7 @@ inline var inv_Phi(const var& p) {
  */
 template <typename T, require_var_matrix_t<T>* = nullptr>
 inline auto inv_Phi(const T& p) {
-  const auto& arena_rtn = to_arena(inv_Phi(p.val()));
+  auto arena_rtn = to_arena(inv_Phi(p.val()));
   return make_callback_var(arena_rtn, [p, arena_rtn](auto& vi) mutable {
     auto deriv
         = arena_rtn.unaryExpr([](auto x) { return exp(-std_normal_lpdf(x)); });

stan/math/rev/prob/std_normal_log_qf.hpp

@@ -19,7 +19,7 @@ namespace math {
  */
 template <typename T, require_stan_scalar_or_eigen_t<T>* = nullptr>
 inline auto std_normal_log_qf(const var_value<T>& log_p) {
-  const auto& arena_rtn = to_arena(std_normal_log_qf(log_p.val()));
+  auto arena_rtn = to_arena(std_normal_log_qf(log_p.val()));
   return make_callback_var(arena_rtn, [log_p, arena_rtn](auto& vi) mutable {
     if constexpr (is_eigen<decltype(arena_rtn)>::value) {
       auto deriv = exp(log_p.val() - arena_rtn.unaryExpr([](auto x) {