Drop generating "compat setter pointer" for optional map thrift fileds

Summary:
Modernizing code generator for Go

#build_rule_type[go_library,go_binary,go_unittest,go_test]

Reviewed By: echistyakov

Differential Revision: D68407033

fbshipit-source-id: 24b7508008cfbdef41254c8d23ed75138952a725

thrift/compiler/generate/t_mstch_go_generator.cc

@@ -437,9 +437,7 @@ class mstch_go_field : public mstch_field {
     // This method helps with backwards compatibility.
     bool has_default_value = (field_->default_value() != nullptr);
     if (is_optional_() && has_default_value) {
-      auto real_type = field_->type()->get_true_type();
-      bool is_container = real_type->is_map();
-      return is_container;
+      return false;
     }
     return is_pointer_();
   }