systemc: Remove a redundant call to update() from the kernel object.

systemc: Remove a redundant call to update() from the kernel object.

The t0Handler runs the scheduler's initPhase function which has a call
to update built into it. There's no reason to call that within one of
the kernel's callbacks as well.

Change-Id: I02c755b7d53f93accdacf8149cc1988d7a6e214c
Reviewed-on: https://gem5-review.googlesource.com/c/12604
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>