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.
if the formal owner of this code (core) @ktf , @Dr15Jones , @davidlange6 agree and support your request I will (remove the two commented line at this point)