[lld-macho][nfc] Removed unnecessary static_cast

[int3]

Thanks!

lld/MachO/Symbols.h

enum Kind {
     UndefinedKind,
     CommonKind,
     DylibKind,
     LazyKind,
   };
 
   virtual ~Symbol() {}
 
-  Kind kind() const { return static_cast<Kind>(symbolKind); }
+  Kind kind() const { return symbolKind; }
 
   StringRef getName() const {
     if (nameSize == (uint32_t)-1)
       nameSize = strlen(nameData);
     return {nameData, nameSize};
   }
 
   virtual uint64_t getVA() const { return 0; }