Changed implementation of getColoursNotUsedByVerticeNeighbours and removed call to changeVerticeColourToAnotherAvailableColour

Results 7,3,7,7,7,7, [38/60]
changed the implementation of getColoursNotUsedByVerticeNeighbours so
it used the method of determining free colours in the incorrect
changeVerticeColourToAnotherAvailableColour
- also removed call to changeVerticeColourToAnotherAvailableColour so
this wasn't being done twice