Stop using bdwidth while printing, work without it

bdwidth's motion reading stays at 0, its per-reading width compensation
made the flow jump between 77 and 119%, and a USB dropout shut down
Klipper. PRINT_START no longer enables it. _PRINT_CLEANUP,
BLOBIFIER_CHECKED and PURGE_UNTIL_EMPTY only send bdwidth commands when
[bdwidth fila_width_0] exists, and bdwidth_status reports present: False
with neutral values when it is not configured, so the section can be
removed from printer.cfg.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

extras/bdwidth_status.py

@@ -26,6 +26,9 @@
 #                    only starts reading on the first SET_BDWIDTH ... ENABLE
 #   linear_motion  - counts per mm (motion_linear_coefficient)
 #   sample_time    - seconds between sensor reads
+#   present        - False when no [bdwidth <sensor>] is configured; the
+#                    other fields then hold neutral defaults, so macros keep
+#                    working with bdwidth removed from the config
 #   usb_ok         - False while the USB connection is down (port: usb)
 #   usb_errors     - USB read errors since Klipper start
 #
@@ -54,7 +57,10 @@ class BDWidthStatus:
                                             self._handle_connect)
 
     def _handle_connect(self):
-        self.sensor = self.printer.lookup_object(self.sensor_name)
+        self.sensor = self.printer.lookup_object(self.sensor_name, None)
+        if self.sensor is None:
+            logging.info("bdwidth_status: no [%s] configured", self.sensor_name)
+            return
         if (getattr(self.sensor, 'port', None) == 'usb'
                 and callable(getattr(self.sensor, 'Read_bdwidth', None))
                 and getattr(self.sensor, 'usb', None) is not None):
@@ -96,6 +102,11 @@ class BDWidthStatus:
 
     def get_status(self, eventtime):
         s = self.sensor
+        if s is None:
+            return {'name': self.name, 'present': False, 'reading': False,
+                    'enabled': False, 'total_move': 0, 'last_motion': 0,
+                    'diameter': 0., 'active': 'disable', 'linear_motion': 42.8,
+                    'sample_time': 1., 'usb_ok': True, 'usb_errors': 0}
         # bdwidth's own get_status() is the runout helper's, which carries
         # the SET_FILAMENT_SENSOR enable flag
         try:
@@ -110,6 +121,7 @@ class BDWidthStatus:
                    and 'disable' not in str(getattr(s, 'is_active', 'disable')))
         return {
             'name': self.name,
+            'present': True,
             'reading': reading,
             'enabled': enabled,
             'total_move': getattr(s, 'actual_total_move', 0),