Always use fully expanded FQME throughout `.clearing`

Since crypto backends now also may expand an FQME like `xbteur.kraken`
-> `xbteur.spot.kraken` (by filling in the venue token), we need to use
this identifier when looking up per-market order dialogs or submitting
new requests. The simple fix is to simply look up that expanded from
from the `Feed.flumes` table which is always keyed by the `MktPair.fqme:
str` - the expanded form.

piker/clearing/_util.py

@@ -91,6 +91,3 @@ class OrderDialogs(Struct):
 
         '''
         return self._flows.pop(oid)
-
-
-