Update on "[ExecuTorch] Add broadcast support for optimized add op"

Summary:
This brings add op to feature parity, wrt, broadcasting, to mul op in
optimized kernels lib

Test Plan:
tests added

Reviewers:

Subscribers:

Tasks:

Tags:

cc larryliu0820 manuelcandales

Differential Revision: [D69491814](https://our.internmc.facebook.com/intern/diff/D69491814)

[ghstack-poisoned]

Author: kimishpatel

kernels/optimized/cpu/op_add.cpp

@@ -140,7 +140,6 @@ Tensor& opt_add_out(
           out.numel());
     });
   } else if (selected_optimized_path != ElementwiseOptimizedPath::kNone) {
-    ScalarType out_type = out.scalar_type();
     ET_SWITCH_REALB_TYPES(out_type, ctx, "add.out", CTYPE, [&]() {
       CTYPE alpha_val;
       ET_KERNEL_CHECK_MSG(

kernels/optimized/cpu/op_mul.cpp

@@ -130,7 +130,6 @@ Tensor& opt_mul_out(
           out.numel());
     });
   } else if (selected_optimized_path != ElementwiseOptimizedPath::kNone) {
-    ScalarType out_type = out.scalar_type();
     ET_SWITCH_REALB_TYPES(out_type, ctx, "mul.out", CTYPE, [&]() {
       auto mul_lambda = [](auto x, auto y) { return x * y; };
       return torch::executor::handle_broadcast_elementwise<CTYPE>(