Make SwitchInstProfUpdateWrapper strict permanently

We have been using -switch-inst-prof-update-wrapper-strict
set to true by default for some time. It is time to remove
the safety stuff and make SwitchInstProfUpdateWrapper
intolerant to inconsistencies in !prof branch_weights
metadata of SwitchInst.

This patch gets rid of the Invalid state of
SwitchInstProfUpdateWrapper and the option
-switch-inst-prof-update-wrapper-strict. So there is only
two states: changed and unchanged.

Reviewers: davidx, nikic, eraman, reames, chandlerc
Reviewed By: davidx
Differential Revision: https://reviews.llvm.org/D67435

llvm-svn: 371707