Make the code that updates ScalarEvolution's internal state in response

to a loop deletion more thorough. Don't prune the def-use tree search at
instructions that don't have SCEVs computed, because an instruction with
a user that has a computed SCEV may itself lack a computed SCEV.  Also,
remove loop-related values from the ValuesAtScopes and
ConstantEvolutionLoopExitValues maps as well.

This fixes a regression in 483.xalancbmk.

llvm-svn: 75030