Remove the custom motd, and stop asserting a guess as the cause

Two problems, one of them mine twice over.

The motd is gone entirely. It had been wrong in a way that mattered — telling
anyone who logged in that onboard WiFi worked when it does not — and a login
banner is a bad place to keep claims that need revising every time we learn
something.

The worse issue is what it and the docs said about why the modem fails. I
inferred from the WOA-Project repository being named "Qualcomm-Reference-
Drivers" that its modem image was a generic reference build unsuited to this
machine's radio, and wrote that up as the explanation. That was a guess resting
on a repository name, and the naming is about redistribution rather than the
contents. Removed from both README and docs/firmware.md.

What is actually established stays: the modem boots, loads mpss, and dies at
"RF stuck in QLINK start state", roughly every 42 seconds. The cause is not
known. The machine has a SIM slot and its modem worked under Windows, so the
radio hardware is present — and the same cabinets supply the GPU, DSP and venus
firmware, all of which work, so whatever is wrong is specific to the modem.
The docs now say that and stop there.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XWRjNJMistCy6ngXH5aJLS

docs/firmware.md

@@ -216,10 +216,15 @@ qcom-q6v5-mss 4080000.remoteproc: fatal error received:
 remoteproc remoteproc0: crash detected ... recovering
 ```
 
-QLINK is the RF front-end interface, and RF front-end wiring is board-specific
-in a way the DSP and GPU images are not. The WOA-Project cabinets are Qualcomm
-*reference* drivers: good enough for the SoC-level blobs, evidently not for this
-machine's radio. It restarts about every 42 seconds until stopped.
+QLINK is the RF front-end interface. Why it hangs is **not established**. The
+machine has a SIM slot and its modem worked under Windows, so the radio hardware
+is present and functional — this is not a WiFi-only SKU. Candidates worth
+investigating: a version mismatch between these images and what the device's
+TrustZone or boot chain expects, missing calibration data the modem cannot
+reach, or a kernel-side gap. It restarts about every 42 seconds until stopped.
+
+Note the same cabinets supply the GPU, DSP and venus firmware, all of which
+work. Whatever is wrong is specific to the modem.
 
 Things that sound like they should help and do not: