[algorithm] Remove use of Prefix

New beat.cmdline tests don't need it anymore

beat/backend/python/algorithm.py

@@ -857,12 +857,9 @@ class Algorithm(object):
         if not self.valid:
             raise RuntimeError("algorithm is not valid")
 
-        if isinstance(prefix, six.string_types):
-            prefix = utils.Prefix(prefix)
-
-        if prefix.paths[0] in self.prefix.paths:
-            raise RuntimeError("Cannot export algorithm to the same prefix (%s in " \
-                    "%s)" % (prefix.paths[0], self.prefix.paths))
+        if prefix == self.prefix:
+            raise RuntimeError("Cannot export algorithm to the same prefix ("
+                               "%s)" % prefix)
 
         for k in self.libraries.values():
             k.export(prefix)