Remove workarounds to make device equality work. (#338)

- dpcpp 2021.2 fixed device equality in the dpcpp runtime and we can
    now remove several workarounds in dpctl:

    - DPCTLDeviceMgr_GetDeviceAndContextPair is now renamed as
      DPCTLDeviceMgr_GetCachedContext and only returns a
      DPCTLSyclContextRef instead of a pair of DPCTLSyclContextRef
      and DPCTLSyclDeviceRef.
    - Remove the DPCTLDeviceMgr_AreEq function and related internal
      helper functions for hashing SYCL devices.
    - Remove DeviceWrapper class inside dpctl_sycl_device_manager.cpp.
    - Remove DPCTL_DeviceAndContextPair type form C API.

  - Make equivalent changes to the Python API.

Author: Diptorup Deb

dpctl/_sycl_queue.pyx

@@ -25,7 +25,10 @@ from ._backend cimport (
     _arg_data_type,
     _backend_type,
     _queue_property_type,
+<<<<<<< HEAD
     DPCTLContext_Create,
+=======
+>>>>>>> Remove workarounds to make device equality work. (#338)
     DPCTLContext_Delete,
     DPCTLDefaultSelector_Create,
     DPCTLDevice_CreateFromSelector,