Remove note about using atomic in host code

- atomic constructor requires multi_ptr
- neither multi_ptr nor atomic are available to the host (Section 4.2)

Using C++11 std::atomic may still make sense for the host device.

Author: Pennycook

latex/programming_interface.tex

@@ -3205,8 +3205,7 @@ \section{Synchronization and atomics}
 library syntax. The only available ordering, due to constraints of the
 OpenCL 1.2 memory model, is \codeinline{memory_order_relaxed}.
 The SYCL atomic library may map directly to
-the underlying C++11 library in host code, and must interact safely
-with the host C++11 atomic library when used in host code. The SYCL
+the underlying C++11 library on the host device. The SYCL
 library must be used in device code to ensure that only the limited
 subset of functionality is available. SYCL 1.2.1 device compilers should
 give a compilation error on use of the \codeinline{std::atomic}