Revert "Add a target legalize hook for SplitVectorOperand"

This reverts commit 187198. It broke the bots.

The soft float test probably needs a -triple because of name differences.
On the hard float test I am getting a "roundss $1, %xmm0, %xmm0", instead of
"vroundss $1, %xmm0, %xmm0, %xmm0".