Simplify implementation by use lambda as a deleter per @AlexanderKalistratov suggestion

Author: oleksandr-pavlyk

examples/pybind11/external_usm_allocation/external_usm_allocation/_usm_alloc_example.cpp

@@ -121,37 +121,21 @@ py::list tolist(DMatrix &m)
     return rows;
 }
 
-class USMDeleter
-{
-public:
-    USMDeleter() = delete;
-    USMDeleter(const USMDeleter &) = default;
-    USMDeleter(USMDeleter &&) = default;
-    USMDeleter(const ::sycl::queue &queue) : _context(queue.get_context()) {}
-    USMDeleter(const ::sycl::context &context) : _context(context) {}
-
-    /*! @brief call operator to delete resources */
-    template <typename T> void operator()(T *ptr) const
-    {
-        try {
-            ::sycl::free(ptr, _context);
-        } catch (const std::exception &e) {
-            std::cout << "Call to sycl::free caught an exception: " << e.what()
-                      << std::endl;
-        }
-    }
-
-private:
-    ::sycl::context _context;
-};
-
 dpctl::memory::usm_memory make_zeroed_device_memory(size_t nbytes,
                                                     sycl::queue &q)
 {
     char *data = sycl::malloc_device<char>(nbytes, q);
     q.memset(data, 0, nbytes).wait();
 
-    USMDeleter _deleter(q);
+    const sycl::context &ctx = q.get_context();
+    auto _deleter = [ctx](void *ptr) {
+        try {
+            ::sycl::free(ptr, ctx);
+        } catch (const std::exception &e) {
+            std::cout << "Call to sycl::free caught an exception: " << e.what()
+                      << std::endl;
+        }
+    };
     auto shptr = std::shared_ptr<void>(data, _deleter);
 
     return dpctl::memory::usm_memory(data, nbytes, q, shptr);