Remove TracerTask

Its brewpi.mat output had no consumer - the GUI never subscribed to the
'Tracer' channel, and SudLogTask's run-scoped JSON logs now cover the same
sensor/heater/tc data for actual analysis. Drop the task, its DT_TASK_TRACER
interval, and the wiring in server/brewpi.py.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DkkuG48uHFCGKe6dPSERFk

tasks/__init__.py

@@ -4,6 +4,5 @@ from tasks.heater import *
 from tasks.stirrer import *
 from tasks.pot import *
 from tasks.tempctrl import *
-from tasks.tracer import *
 from tasks.sud import *
 from tasks.sud_log import *