[SelectionDAG] Remove some dead code from vector scalaring

Summary:
Currently ScalarizeVecRes_SETCC checks for the result type being a vector and jumps to ScalarizeVecRes_VSETCC. But if we're scalarizing a vector result, aren't we guaranteed to be looking at a vector type?

This patch deletes the current ScalarizeVecRes_SETCC and renames  ScalarizeVecRes_VSETCC to ScalarizeVecRes_SETCC.

Reviewers: RKSimon, arsenm, eladcohen, zvi

Reviewed By: RKSimon

Subscribers: wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D40452

llvm-svn: 318982