THRIFT-5576: fix old-style cast and redundant copy

[kashirin-alex]

Generated was:

class FU_LB : public virtual ::apache::thrift::TBase {
 public:

  FU_LB(const FU_LB&);
  FU_LB(FU_LB&&) noexcept;
  FU_LB& operator=(const FU_LB&);
  FU_LB& operator=(FU_LB&&) noexcept;
  FU_LB() noexcept
        : ctrl(0),
          op((FU_LIST_OP::type)0),
          pos(0) {
    op = (FU_LIST_OP::type)0;

  }

  virtual ~FU_LB() noexcept;

Generated became:

class FU_LB : public virtual ::apache::thrift::TBase {
public:

 FU_LB(const FU_LB&);
 FU_LB(FU_LB&&) noexcept;
 FU_LB& operator=(const FU_LB&);
 FU_LB& operator=(FU_LB&&) noexcept;
 FU_LB() noexcept
       : ctrl(0),
         op(static_cast<FU_LIST_OP::type>(0)),
         pos(0) {
 }

 virtual ~FU_LB() noexcept;

[ctubbsii]

For convenience, the diff between the two above are:

@@ -7,10 +7,8 @@
   FU_LB& operator=(FU_LB&&) noexcept;
   FU_LB() noexcept
         : ctrl(0),
-          op((FU_LIST_OP::type)0),
+          op(static_cast<FU_LIST_OP::type>(0)),
           pos(0) {
-    op = (FU_LIST_OP::type)0;
-
   }
 
   virtual ~FU_LB() noexcept;