[clang][dataflow] Remove obsolete FIXME

[sgatev]

Summary

The FIXME is no longer relevant as ControlFlowContext centralizes the
construction of the CFG.

This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.

[xazax.hun]

I think for trivial changes like this you do not need to create a review, you can commit it directly :)

clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp

TypeErasedDataflowAnalysisState transferBlock(
   }
   return State;
 }
 
 std::vector<llvm::Optional<TypeErasedDataflowAnalysisState>>
 runTypeErasedDataflowAnalysis(const ControlFlowContext &CFCtx,
                               TypeErasedDataflowAnalysis &Analysis,
                               const Environment &InitEnv) {
-  // FIXME: Consider enforcing that `Cfg` meets the requirements that
-  // are specified in the header. This could be done by remembering
-  // what options were used to build `Cfg` and asserting on them here.
-
   PostOrderCFGView POV(&CFCtx.getCFG());
   ForwardDataflowWorklist Worklist(CFCtx.getCFG(), &POV);
 
   std::vector<llvm::Optional<TypeErasedDataflowAnalysisState>> BlockStates;
   BlockStates.resize(CFCtx.getCFG().size(), llvm::None);
 
   // The entry basic block doesn't contain statements so it can be skipped.
   const CFGBlock &Entry = CFCtx.getCFG().getEntry();