mem: Remove the ContextSwitchTaskId namespace

This namespace has gone through the deprecation period
and can now be removed.

Change-Id: Iab4bb6ac6e8d603fb508330691796ccdac4b9cb6
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67357
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

src/mem/request.hh

@@ -74,7 +74,6 @@ namespace gem5
  * doesn't cause a problem with stats and is large enough to realistic
  * benchmarks (Linux/Android boot, BBench, etc.)
  */
-GEM5_DEPRECATED_NAMESPACE(ContextSwitchTaskId, context_switch_task_id);
 namespace context_switch_task_id
 {
     enum TaskId