Revert "[VectorUtils] Query number of sign bits to allow more truncations"

This was a fairly simple patch but on closer inspection was seriously flawed and caused PR27690.

This reverts commit r268921.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269051 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed