tests/kernel/fatal/exception: Remove ticked kernel from stack sentinel test

The "sentinel" variant of this test runs the same code, but enables
the stack sentinel feature.  Inexplicably, it's also disabling
TICKLESS_KERNEL, forcing a timer interrupt at every tick boundary.

That doesn't seem to be required for any test functionality I can see.

And worse, by changing that setting without adjusting the tick rate,
it runs afoul of more modern platforms which were designed with
tickless operation in mind.  Specifically, the intel_adsp platforms
have a default tick rate of 50 kHz, which is just too fast for
reasonable operation.  It leaves almost no time available for
application code and something falls behind and fails.

Just remove it.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>