ci: testbed: stop installing packages at runtime

The shared testbed setup installs MiniDLNA, Avahi, and dbus before
every cram and CDRouter job. This adds network and package mirror
dependencies to hardware tests and allows the runtime environment to
drift independently of the selected image.

The separately released testbed image now carries these packages,
together with the Python dependencies used by cram. Remove the runtime
apt update and install command so jobs consume only the image contents.

Assisted-by: codex:gpt-5
Signed-off-by: Petr Štetiar <petr.stetiar@prplfoundation.org>
Fixes: 6792ba6b95 ("PROVISORY: ci: testbed: install minidlna and avahi packages at runtime")
References: PPW-1258

.gitlab/testbed.yml

@@ -59,8 +59,6 @@
     - sudo ip link set $TESTBED_WAN_INTERFACE up 2> /dev/null
     - sleep 10
 
-    - sudo apt-get update && sudo apt-get install --yes --no-install-recommends minidlna avahi-daemon avahi-utils dbus
-
     - mkdir -p ~/.ssh
     - chmod 700 ~/.ssh