Eliminate extraneous {};

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@124456 91177308-0d34-0410-b5e6-96231b3b80d8

include/type_traits

@@ -602,8 +602,6 @@ template <class _Tp> struct _LIBCPP_VISIBLE is_abstract : public __libcpp_abstra
 
 template <class _T1, class _T2> struct _LIBCPP_VISIBLE is_convertible
     : public integral_constant<bool, __is_convertible_to(_T1, _T2)> {};
-{
-};
 
 #else  // __clang__