sim: Remove the Enums namespace

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

Change-Id: If4daad57a421b076ae6661812c2255c7f06f30b9
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67372
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

build_tools/enum_cc.py

@@ -97,8 +97,7 @@ const char *${name}Strings[static_cast<int>(${name}::Num_${name})] =
         )
     else:
         code(
-            """GEM5_DEPRECATED_NAMESPACE(Enums, enums);
-namespace enums
+            """namespace enums
 {"""
         )
         code.indent(1)