Revert "Fix Apple-specific XFAIL directive in libc++ test"

This reverts commit r296712. It broke our bot.

It turns out that the test is passing with c++11 and c++14 but
not c++1z on this particular version of the compiler. Since one
job is defaulting to c++1z and the other is testing all config I'm
not sure how to fix this...

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@296724 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed