Revert r294356, "DebugInfo: Track spilled variables in LiveDebugValues"

It caused undefined behavior in VarLoc. As far as I investigated,

  - VarLoc::VarLoc() treats negative offset value as InvalidKind.
    Consider the case that (int64_t)MI.getOperand(1).getImm() is negative and whether it satisfies ((uint64_t)Offset < (1ULL << 32)).

  - Comparison operators in VarLoc behave undefined since VarLoc::Loc.Hash is uninitialized in case of InvalidKind.

I guess Offset (in VarLoc) could be made aware of signed, but I am not sure.
So I have reverted it for now.

llvm-svn: 294447