[Polly] Remove usage of the `apply` function

[sanjoy]

Summary

API-wise apply is a somewhat unidiomatic one-off function, and
removing the only(?) use in polly will let me remove it from SCEV's
exposed interface.

[grosser]

LGTM.

lib/CodeGen/BlockGenerators.cpp

Value *BlockGenerator::trySynthesizeNewValue(ScopStmt &Stmt, Value *Old,
 
   const SCEV *Scev = SE.getSCEVAtScope(Old, L);
   if (!Scev)
     return nullptr;
 
   if (isa<SCEVCouldNotCompute>(Scev))
     return nullptr;
 
-  const SCEV *NewScev = apply(Scev, LTS, SE);
+  const SCEV *NewScev = SCEVLoopAddRecRewriter::rewrite(Scev, LTS, SE);
   ValueMapT VTV;
   VTV.insert(BBMap.begin(), BBMap.end());
   VTV.insert(GlobalMap.begin(), GlobalMap.end());
 
   Scop &S = *Stmt.getParent();
   const DataLayout &DL = S.getFunction().getParent()->getDataLayout();
   auto IP = Builder.GetInsertPoint();