Backend code cleanup (#2485)

The PR removes unused code from the backend:

- `DPNPC_id` and `DPNP_USM_iterator` classes
- `LIBSYCL_VERSION_GREATER` macro
- `broadcastable` and `get_validated_axes` header functions
- `dpnp_iterator.hpp` header file

GTests for removed functions are also cleaned up.

Author: antonwolfy

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Adjusted the `pre-commit` configuration to run autoupdate weekly [#2479](https://github.com/IntelPython/dpnp/pull/2479)
 * Improved validation of `--target-hip` build option to only accept a gfx-prefixed value [#2481](https://github.com/IntelPython/dpnp/pull/2481)
+* Cleaned up backend code to remove obsolete and unused parts of functionality [#2485](https://github.com/IntelPython/dpnp/pull/2485)
 
 ### Fixed
 

dpnp/backend/kernels/dpnp_krnl_mathematical.cpp

@@ -30,7 +30,6 @@
 #include <dpnp_iface.hpp>
 
 #include "dpnp_fptr.hpp"
-#include "dpnp_iterator.hpp"
 #include "dpnp_utils.hpp"
 #include "dpnpc_memory_adapter.hpp"
 #include "queue_sycl.hpp"