[libc++][NFC] Remove an outdated UNSUPPORTED annotation

This is likely a rebase artifact. libcpp-has-no-concepts is not a
Lit feature we ever define anymore.

Author: ldionne

libcxx/test/std/iterators/predef.iterators/move.iterators/move.iter.ops/move.iter.op.comp/op_spaceship.pass.cpp

@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
-// UNSUPPORTED: libcpp-has-no-concepts
 
 // <iterator>