Revert "[libc++] Fix PR35491 - std::array of zero-size doesn't work with non-default constructible types."

Revert "Fix initialization of array<const T, 0> with GCC."
Revert "Make array<const T, 0> non-CopyAssignable and make swap and fill ill-formed."

This reverts commit r324182, r324185, and r324194 which were causing issues with zero-length std::arrays.

llvm-svn: 324309

libcxx/test/std/containers/sequences/array/array.data/data_const.pass.cpp

@@ -38,16 +38,6 @@ int main()
         const T* p = c.data();
         (void)p; // to placate scan-build
     }
-    {
-      struct NoDefault {
-        NoDefault(int) {}
-      };
-      typedef NoDefault T;
-      typedef std::array<T, 0> C;
-      const C c = {};
-      const T* p = c.data();
-      assert(p != nullptr);
-    }
 #if TEST_STD_VER > 14
     {
         typedef std::array<int, 5> C;