configs: Remove unneeded variable assignments in apu_se

This patch removes:
A line assigning a variable to itself

An assignment to a variable (chroot) that is never used.
The above assignment also caused an error, "'NoneType' object
has no attribute 'startswith'"

Change-Id: Ib93c25fee4a0f7c1440de8067b086d8b96614796
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32654
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

configs/example/apu_se.py

@@ -334,8 +334,6 @@ for i in range(n_cu):
 shader.CUs = compute_units
 
 ########################## Creating the CPU system ########################
-options.num_cpus = options.num_cpus
-
 # The shader core will be whatever is after the CPU cores are accounted for
 shader_idx = options.num_cpus
 
@@ -616,7 +614,6 @@ else:
 
 ########################## Start simulation ########################
 
-chroot = os.path.expanduser(options.chroot)
 redirect_paths = [RedirectPath(src = "/proc",
                                dests = ["%s/fs/proc" % m5.options.outdir]),
                   RedirectPath(src = "/sys",