[SYCL][NFC] Remove outdated TODO comment (#2770)

`cl::sycl::half` has been added to the specification by
KhronosGroup/SYCL-Docs#83.

Author: bader

sycl/include/CL/sycl/aliases.hpp

@@ -79,8 +79,6 @@ using uint = unsigned int;
 using ulong = unsigned long;
 using longlong = long long;
 using ulonglong = unsigned long long;
-// TODO cl::sycl::half is not in SYCL specification, but is used by Khronos CTS.
-// Related tests issue: KhronosGroup/SYCL-CTS#37
 using half = cl::sycl::detail::half_impl::half;
 using cl_bool = bool;
 using cl_char = std::int8_t;