Revert "[InstCombine] Fix visitSwitchInst to use right operand types for sub cstexpr"

Reverts commit r224574 to appease buildbots:

The visitSwitchInst generates SUB constant expressions to recompute the
switch condition. When truncating the condition to a smaller type, SUB
expressions should use the previous type (before trunc) for both
operands. This fixes an assertion crash.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224576 91177308-0d34-0410-b5e6-96231b3b80d8