Revert "numpy.h: minor preprocessor fix suggested by @chaekwan"

This reverts commit 61e4f1182357cc0f55b567b128011c579e4c7ccd.

include/pybind11/numpy.h

diff --git a/include/pybind11/numpy.h b/include/pybind11/numpy.h
index c544c54..ba41a22 100644
--- a/include/pybind11/numpy.h
+++ b/include/pybind11/numpy.h
@@ -311,7 +311,7 @@
 
 template <typename T> using is_pod_struct = all_of<
     std::is_standard_layout<T>,     // since we're accessing directly in memory we need a standard layout type
-#if !defined(__GNUG__) || defined(_LIBCPP_VERSION) || (defined(_GLIBCXX_USE_CXX11_ABI) && _GLIBCXX_USE_CXX11_ABI != 0)
+#if !defined(__GNUG__) || defined(_LIBCPP_VERSION) || defined(_GLIBCXX_USE_CXX11_ABI)
     // _GLIBCXX_USE_CXX11_ABI indicates that we're using libstdc++ from GCC 5 or newer, independent
     // of the actual compiler (Clang can also use libstdc++, but it always defines __GNUC__ == 4).
     std::is_trivially_copyable<T>,