profiles: Descent 3 runs a blank greeting

Synced from the canonical copy in the game's repo: the pod display stays dark
from activation until the game sends the pilot's callsign.

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

profiles/descent3.json

@@ -3,7 +3,7 @@
   "MatchExecutables": [ "Descent3" ],
   "RioComPort": "COM1",
   "PlasmaComPort": "COM2",
-  "PlasmaGreeting": "DESCENT 3",
+  "PlasmaGreeting": null,
   "WallpaperPath": null,
   "Calibration": {
     "InvertX": false,