setdiscovery: drop '_setupsample' usage in '_takequicksample'

For '_takefullsample' we can just retrieve the list of head directly and
ignore the rest of the complex return values. This was the last call to the
infamous '_updatesample' function.

mercurial/setdiscovery.py

@@ -95,10 +95,9 b' def _setupsample(dag, nodes, size):'
     return always, set(), desiredlen
 
 def _takequicksample(dag, nodes, size):
-    always, sample, desiredlen = _setupsample(dag, nodes, size)
-    if sample is None:
-        return always
-    sample = always
+    sample = dag.headsetofconnecteds(nodes)
+    if size <= len(sample):
+        return _limitsample(sample, size)
     _updatesample(dag, None, sample, quicksamplesize=size)
     return sample