cpu: Clear out some unnecessary ISA dependence in thread_context.hh.

The ISA version of the ISA class isn't used any more. Neither is
TheISA::MachInst.

Change-Id: I9085ad2b51ba19bf6e5bb17769dd048ac6384fec
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34821
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed