[ValueLattice] Remove obsolete getConstantInt (NFC).

[fhahn]

Summary

ConstantInt values are always represented as constant ranges with a
single element. getConstantInt is obsolete, as pointed out by @nikic
during D60581.

[nikic]

LG

llvm/include/llvm/Analysis/ValueLattice.h

if (NewR.isFullSet())
       markOverdefined();
     else if (NewR == getConstantRange())
       return false;
     else
       markConstantRange(std::move(NewR));
     return true;
   }
 
-  ConstantInt *getConstantInt() const {
-    assert(isConstant() && isa<ConstantInt>(getConstant()) &&
-           "No integer constant");
-    return cast<ConstantInt>(getConstant());
-  }
-
   /// Compares this symbolic value with Other using Pred and returns either
   /// true, false or undef constants, or nullptr if the comparison cannot be
   /// evaluated.
   Constant *getCompare(CmpInst::Predicate Pred, Type *Ty,
                        const ValueLatticeElement &Other) const {
     if (isUndefined() || Other.isUndefined())
       return UndefValue::get(Ty);