test/hil: fail audio test on missing alsa-utils instead of skipping

arecord (alsa-utils) is a documented HIL host requirement, like
mtools/libmtp9/iperf — none of which have a skip-if-missing guard. The
audio test was the exception: it silently returned 'skipped' when arecord
was absent, masking host misconfiguration. The ci.lan rig had been
silently skipping device/audio_test_freertos on every board because
alsa-utils was never installed.

Remove the shutil.which('arecord') guard so a missing package surfaces as
a failure, consistent with the other tool-dependent tests, and drop the
now-unused shutil import. Note in the host-setup comment that these
packages are required (a missing tool fails its test rather than skipping).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/hil/hil_test.py

@@ -22,7 +22,7 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
-# Host setup:
+# Host setup (required: a missing tool fails its test rather than skipping it):
 #   - System packages: sudo apt install mtools libmtp9 alsa-utils iperf
 #       mtools     - read_disk_file (device/cdc_msc, device/msc_dual_lun)
 #       libmtp9    - pymtp ctypes load (device/mtp); Debian 13 uses libmtp9t64
@@ -51,7 +51,6 @@ import serial
 import subprocess
 import json
 import glob
-import shutil
 from multiprocessing import Pool, Lock
 from multiprocessing import TimeoutError as MpTimeoutError
 import hashlib
@@ -1380,10 +1379,6 @@ def test_device_audio_test_freertos(board):
     if os.name == 'nt':
         return 'skipped'
 
-    arecord = shutil.which('arecord')
-    if arecord is None:
-        return 'skipped'
-
     pcm = None
     timeout = ENUM_TIMEOUT
     while timeout > 0:
@@ -1397,7 +1392,7 @@ def test_device_audio_test_freertos(board):
 
     raw_path = f'/tmp/tinyusb_audio_{uid}.raw'
     cmd = [
-        arecord,
+        'arecord',
         '-D', pcm,
         '-q',
         '-f', 'S16_LE',