Remove dead host esszimmerradio

The Pi is gone; the name no longer resolves. It was still picked up by
the "hosts: all" playbooks (update-packages.yml, test_keepass.yml),
where it showed up as unreachable on every fleet run.

It was also the only host pointing pi_squeezelite_squeezeserver at
192.168.178.100 (musicdolphin) rather than the central server at .80,
so nothing depends on musicdolphin's LMS instance any more.

The "esszimmer" rows in roles/bluetooth_monitor/other/*.csv and the
analysis notebook are room labels in historical sensor training data,
not this host, and are left alone.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

roles/pi_standard_setup/files/motd/esszimmerradio

@@ -1,12 +0,0 @@
-  EsszimmerRadio Eltern
-  
-       ________
-      /______  |
-     |       | |      _
-     | ===== | |     | |
-     | ===== | |    o o
-     |       | |         |~
-     |  .-.  | |       o    o o
-     | ' . ' | |   |~       |_|
-  ..'| '._.' | |  o
-.'   |_______|/