[SPARK-4797] Replace breezeSquaredDistance

This PR replaces slow breezeSquaredDistance. A simple calculation involving 40000 squared distances between the vectors of 20000 dims shows:

* breezeSquaredDistance:  ~12 secs
* This PR: ~10.5 secs


No need to check ```(kv1 < nnzv1 && kv2 < nnzv2)``` here since it will always be true (because of the previous 2 if statements).