WebXR: point to the public chromium-webxr-steam-frame repo

The build script, launcher and Steam shortcut helper now live in
saphid/chromium-webxr-steam-frame, so drop the duplicate copies here.
The doc keeps the findings, verification and upstream status.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

frame/chromium-xr/launch.sh

@@ -1,27 +0,0 @@
-#!/bin/bash
-# Frame-side: start the WebXR Chromium build (~/chromium-xr). The Steam
-# library shortcut "Chromium XR" runs this, and so does
-# `scripts/chromium-xr.sh launch` (which adds a DevTools port). Extra
-# arguments go to Chrome, so a URL opens that page.
-#
-# Lives in ~/Applications/ChromiumXR, outside ~/chromium-xr, so reinstalling
-# the build doesn't delete it.
-set -euo pipefail
-
-CHROME="$HOME/chromium-xr/chrome"
-[[ -x "$CHROME" ]] || { echo "launch.sh: no build at $CHROME (run chromium-xr.sh install)" >&2; exit 1; }
-
-# Without --no-first-run and --password-store=basic, startup can stop at a
-# first-run or keyring prompt.
-# --disable-seccomp-filter-sandbox: under the XR seccomp policy, SteamVR's
-# client reads /proc/self/status through the file broker, gets the broker's
-# pid, and SteamVR binds the app to the wrong process, so xrCreateInstance
-# fails. The namespace sandbox stays on, but seccomp is off for every
-# process, so keep this profile for VR sites.
-exec "$CHROME" \
-  --user-data-dir="$HOME/.config/chromium-xr" \
-  --enable-features=OpenXR \
-  --ozone-platform=x11 \
-  --no-first-run --no-default-browser-check --password-store=basic \
-  --disable-seccomp-filter-sandbox \
-  "$@"