fastmodel: remove incorrect cntfrq update

fastmodel: remove incorrect cntfrq update

The register cntfrq should be set to system counter frequency.
However, the current fastmodel implementation accidentally set it to
core frequency. This CL removes the wrong implementation, and real
cntfrq setting is performed in the initState.

Change-Id: I6c62822a4fbbcc0c499f79f6003dabb0c133f997
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40276
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>