[libcxx] [test] Remove XFAIL LIBCXX-WINDOWS-FIXME from time.clock.file/now.pass.cpp

This doesn't fail when _LIBCPP_HAS_NO_INT128 is defined consistently
in both CMAKE_CXX_FLAGS and LIBCXX_TEST_COMPILER_FLAGS; the XFAIL was
added based on early CI testruns where that flag was missing in
LIBCXX_TEST_COMPILER_FLAGS.

Differential Revision: https://reviews.llvm.org/D99705