remove toposort from pytensor/graph/utils.py it was not referenced anywhere

pytensor/graph/utils.py

@@ -379,44 +379,3 @@ class AssocList:
 
     def __repr__(self):
         return f"AssocList({self._dict}, {self._list})"
-
-
-def toposort(prereqs_d):
-    """
-    Sorts prereqs_d.keys() topologically.
-
-    prereqs_d[x] contains all the elements that must come before x
-    in the ordering.
-
-    """
-
-    #     all1 = set(prereqs_d.keys())
-    #     all2 = set()
-    #     for x, y in prereqs_d.items():
-    #         all2.update(y)
-    #     print all1.difference(all2)
-
-    seq = []
-    done = set()
-    postreqs_d = {}
-    for x, prereqs in prereqs_d.items():
-        for prereq in prereqs:
-            postreqs_d.setdefault(prereq, set()).add(x)
-    next = {k for k in prereqs_d if not prereqs_d[k]}
-    while next:
-        bases = next
-        next = set()
-        for x in bases:
-            done.add(x)
-            seq.append(x)
-        for x in bases:
-            for postreq in postreqs_d.get(x, []):
-                if not prereqs_d[postreq].difference(done):
-                    next.add(postreq)
-    if len(prereqs_d) != len(seq):
-        raise Exception(
-            "Cannot sort topologically: there might be cycles, "
-            "prereqs_d does not have a key for each element or "
-            "some orderings contain invalid elements."
-        )
-    return seq