arch,cpu,sim: Get rid of the microcode ROM stub code.

This code, including a switching header file, is no longer necessary
because ROM based microops are now handled by the decoder itself.

Change-Id: Ie3ea4a7371dec22993ede80e2acd1df7cd1ecf59
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32899
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/cpu/base.hh

@@ -52,7 +52,6 @@
 #else
 #include "arch/generic/interrupts.hh"
 #include "arch/isa_traits.hh"
-#include "arch/microcode_rom.hh"
 #include "base/statistics.hh"
 #include "mem/port_proxy.hh"
 #include "sim/clocked_object.hh"
@@ -213,8 +212,6 @@ class BaseCPU : public ClockedObject
     // @todo remove me after debugging with legion done
     Tick instCount() { return instCnt; }
 
-    TheISA::MicrocodeRom microcodeRom;
-
   protected:
     std::vector<BaseInterrupts*> interrupts;