sim: Delete the unused PowerStateDumpCallback.

Issue-on: https://gem5.atlassian.net/browse/GEM5-698
Change-Id: I8e66f31a3a6a82564d9525021ada49ce52beb1fa
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32646
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/sim/power_state.hh

@@ -151,12 +151,4 @@ class PowerState : public SimObject
     } stats;
 };
 
-class PowerStateDumpCallback : public Callback
-{
-    PowerState *co;
-  public:
-    PowerStateDumpCallback(PowerState *co_t) : co(co_t) {}
-    virtual void process() { co->computeStats(); };
-};
-
 #endif //__SIM_POWER_STATE_HH__