fix(erpnext): remove default 'BC' from Sales Order incorporation_province

The custom_incorporation_province field had default='BC', which stamped 'BC'
on EVERY Sales Order (US trucking, formation, compliance) — not just Canadian
CRTC orders. This leaked a meaningless 'BC' onto e.g. an SC scrap-metal carrier's
order. Removed the default and added a blank option so it's empty unless it's an
actual Canadian incorporation. Existing non-canada_crtc orders cleared in prod
via db_set (13 fixed; the 2 real canada_crtc orders keep BC).

performancewest_erpnext/performancewest_erpnext/fixtures/custom_field.json

@@ -153,8 +153,7 @@
     "fieldname": "custom_incorporation_province",
     "fieldtype": "Select",
     "label": "Incorporation Province",
-    "options": "BC\nON",
-    "default": "BC",
+    "options": "\nBC\nON",
     "insert_after": "custom_incorporation_number"
   },
   {