Add note to `.brokers.ib.api` about removing `_bar_load_dtype`

piker/brokers/ib/api.py

@@ -96,6 +96,10 @@ from ._util import (
     get_logger,
 )
 
+# ?TODO? this can now be removed since it was originally to extend
+# with a `bar_vwap` field that we removed from the default ohlcv
+# dtype since it's better calculated in an FSP func
+#
 _bar_load_dtype: list[tuple[str, type]] = [
     # NOTE XXX: only part that's diff
     # from our default fields where