[SYCL][CUDA][HIP] Remove CUDA and HIP PI unit tests

These tests are not currently running and are covered in other test
suites:

* `test_primary_context.cpp`
  * Deprecated feature, covered in `test-e2e/Basic/context.cpp`
* `test_commands.cpp`
  * Covered by UR CTS
* `test_sampler_properties.cpp`
  * Covered by UR CTS: https://github.com/oneapi-src/unified-runtime/tree/main/test/conformance/sampler
* `PlatformTest.cpp`
  * Covered by UR CTS: https://github.com/oneapi-src/unified-runtime/blob/main/test/conformance/platform/urPlatformGetInfo.cpp
* `test_device.cpp`
  * Covered by UR CTS: https://github.com/oneapi-src/unified-runtime/blob/main/test/conformance/device/urDeviceGetInfo.cpp
* `EnqueueMemTest.cpp`
  * Covered by UR CTS: https://github.com/oneapi-src/unified-runtime/blob/main/test/conformance/enqueue/urEnqueueMemBufferFill.cpp
* `test_mem_obj.cpp`
  * Moved to UR CTS
* `test_contexts.cpp`
  * https://github.com/oneapi-src/unified-runtime/blob/main/test/adapters/cuda/context_tests.cpp
* `test_kernels.cpp`
  * https://github.com/oneapi-src/unified-runtime/blob/main/test/adapters/cuda/kernel_tests.cpp
* `test_base_objects.cpp`
  * Basic tests mostly covered in UR
* `test_interop_get_native.cpp`
  * Mostly covered in UR tests and E2E tests

sycl/unittests/pi/CMakeLists.txt

@@ -1,9 +1,7 @@
 set(CMAKE_CXX_EXTENSIONS OFF)
 
 add_sycl_unittest(PiTests OBJECT
-  EnqueueMemTest.cpp
   PiMock.cpp
-  PlatformTest.cpp
   PiUtility.cpp
   pi_arguments_handler.cpp
   piInteropRetain.cpp
@@ -13,11 +11,3 @@ add_dependencies(PiTests sycl)
 target_include_directories(PiTests PRIVATE SYSTEM ${sycl_inc_dir})
 target_include_directories(PiTests PRIVATE ${sycl_src_dir}/../tools/xpti_helpers)
 
-if("cuda" IN_LIST SYCL_ENABLE_PLUGINS)
-    add_subdirectory(cuda)
-endif()
-
-if("hip" IN_LIST SYCL_ENABLE_PLUGINS)
-    add_subdirectory(hip)
-endif()
-