Removed superfluous ListLink

Hi @cosmoharrigan, I noticed that what we discussed in https://github.com/opencog/opencog/issues/844#issuecomment-45509872 also applies to the deduction-rule: Because the consequence of the ImplicationLink is a ListLink, this ListLink is put into the ListLink produced as the result of ```cog-bind``` and consists now of two identical atoms, the first one the first item of the ListLink, the second one the output of the ExecutionLink (as performed on [this input](https://github.com/sebastianruder/opencog/blob/master/tests/learning/RuleEngine/simple-assertions.scm)):
```
(ListLink (stv 1.000000 0.000000)
  (ListLink (stv 1.000000 0.000000)
    (InheritanceLink (stv inf 0.900000)
      (ConceptNode "Peirce") ; [266]
      (ConceptNode "human") ; [269]
    ) ; [286]
    (InheritanceLink (stv inf 0.900000)
      (ConceptNode "Peirce") ; [266]
      (ConceptNode "human") ; [269]
    ) ; [286]
  ) ; [288]
) ; [289]
```
If we remove the ListLink and the first InheritanceLink, we get a much nicer output:
```
(ListLink
   (InheritanceLink (stv inf 0.89999998)
      (ConceptNode "Peirce")
      (ConceptNode "human")
   )
)
```