riscv: Remove unnecessary includes from arch/riscv/isa_traits.hh.

Change-Id: Iff3e840c5b67fa23ebead337abf323e7add2e6db
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33200
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/riscv/isa_traits.hh

@@ -42,9 +42,7 @@
 #ifndef __ARCH_RISCV_ISA_TRAITS_HH__
 #define __ARCH_RISCV_ISA_TRAITS_HH__
 
-#include "arch/riscv/types.hh"
 #include "base/types.hh"
-#include "cpu/static_inst_fwd.hh"
 
 namespace RiscvISA
 {