faft: Deprecate the broken_warm_reset FAFT config

There are 3 boards using this broken_warm_reset FAFT config to work
around the warm reset problem. Parrot fix is moved to servod, check:
  https://chromium-review.googlesource.com/269138

Butterfly and Stout are not supported currently. If we add support of
them, the changes will go the servod, not FAFT.

So it is safe to deprecate the broken_warm_reset FAFT config.

BUG=chrome-os-partner:39744
TEST=None
CQ-DEPEND=CL:269138

Change-Id: Ib48056dccb1506140aba8d16a0a1c05fb0ed1810
Reviewed-on: https://chromium-review.googlesource.com/269139
Reviewed-by: Yusuf Mohsinally <mohsinally@chromium.org>
Commit-Queue: Tom Tam <waihong@google.com>
Tested-by: Tom Tam <waihong@google.com>
diff --git a/server/cros/faft/firmware_test.py b/server/cros/faft/firmware_test.py
index 5d10dbb..3015247 100644
--- a/server/cros/faft/firmware_test.py
+++ b/server/cros/faft/firmware_test.py
@@ -1060,12 +1060,7 @@
 
         A wrapper for underlying servo warm reset.
         """
-        # Use cold reset if the warm reset is broken.
-        if self.faft_config.broken_warm_reset:
-            logging.info('broken_warm_reset is True. Cold rebooting instead.')
-            self.reboot_cold_trigger()
-        else:
-            self.servo.get_power_state_controller().warm_reset()
+        self.servo.get_power_state_controller().warm_reset()
 
     def reboot_cold_trigger(self):
         """Request a cold reboot.