It hasn't been used since r130964.
This also removes MachineModuleInfo::isUsedFunction and
MachineModuleInfo::AnalyzeModule, both of which were only
there to support UsedFunctions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239501 91177308-0d34-0410-b5e6-96231b3b80d8