back to SSE

Given the current level of optimization and that AVX will be not used in production in 2015 we revert to the SSE version for all vectors.
(also removed an obsolete "pretended to be" SSE-specific code)

Purely technical, no regression expected.

Speed up expected and observed in few routines using double precision four vectors.
Then may I ask you to add this or similar to the comment so the intent and perspectives are clear (there are so many pieces in the code that are apparently left to hang forever with no use)?