Revert "make non-const operator[] method for scalar_seq_view"

This reverts commit bf6e4fd.

Author: hsbadr

stan/math/prim/fun/scalar_seq_view.hpp

@@ -30,7 +30,6 @@ class scalar_seq_view<C, require_eigen_vector_t<C>> {
    * @return the element at the specified position in the container
    */
   inline auto operator[](size_t i) const { return c_.coeff(i); }
-  inline auto& operator[](size_t i) { return c_.coeffRef(i); }
 
   inline auto size() const noexcept { return c_.size(); }
 

stan/math/prim/prob/exp_mod_normal_lccdf.hpp

@@ -66,8 +66,8 @@ return_type_t<T_y, T_loc, T_scale, T_inv_scale> exp_mod_normal_lccdf(
 
   scalar_seq_view<decltype(y_val)> y_vec(y_val);
   for (size_t n = 0, size_y = stan::math::size(y); n < size_y; n++) {
-    if (is_inf(y_vec.val(n))) {
-      return ops_partials.build(y_vec.val(n) > 0 ? negative_infinity() : 0);
+    if (is_inf(y_vec[n])) {
+      return ops_partials.build(y_vec[n] > 0 ? negative_infinity() : 0);
     }
   }
 

stan/math/prim/prob/gamma_lpdf.hpp

@@ -84,7 +84,7 @@ return_type_t<T_y, T_shape, T_inv_scale> gamma_lpdf(const T_y& y,
 
   scalar_seq_view<decltype(y_val)> y_vec(y_val);
   for (size_t n = 0; n < stan::math::size(y); n++) {
-    if (y_vec.val(n) < 0) {
+    if (y_vec[n] < 0) {
       return LOG_ZERO;
     }
   }