file_util: Remove compiler version checks around is_trivially_copyable()

The minimum clang/GCC versions we support already support this. We can also
remove is_standard_layout(), as fread and fwrite only require the type to be
trivially copyable.

src/common/file_util.h

@@ -170,12 +170,8 @@ public:
 
     template <typename T>
     size_t ReadArray(T* data, size_t length) {
-        static_assert(std::is_standard_layout<T>(),
-                      "Given array does not consist of standard layout objects");
-#if (__GNUC__ >= 5) || defined(__clang__) || defined(_MSC_VER)
         static_assert(std::is_trivially_copyable<T>(),
                       "Given array does not consist of trivially copyable objects");
-#endif
 
         if (!IsOpen()) {
             m_good = false;
@@ -191,12 +187,8 @@ public:
 
     template <typename T>
     size_t WriteArray(const T* data, size_t length) {
-        static_assert(std::is_standard_layout<T>(),
-                      "Given array does not consist of standard layout objects");
-#if (__GNUC__ >= 5) || defined(__clang__) || defined(_MSC_VER)
         static_assert(std::is_trivially_copyable<T>(),
                       "Given array does not consist of trivially copyable objects");
-#endif
 
         if (!IsOpen()) {
             m_good = false;