tests: Removed `tests/halt.sh`

tests: Removed `tests/halt.sh`

`tests/halt.sh` is a duplicate of `configs/tests/halt.sh`. The one
instance of using `halt.sh`, `tests/gem5/fs/linux/arm/run.py`, has been
updated to use `configs/tests/halt.sh` and `tests/halt.sh` has been
removed.

Change-Id: I42f77a22b5985959a579c75541e4a0fdc135aa0c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33135
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>