[Analysis] Remove unused forward declarations (NFC)

Author: kazutakahirata

llvm/include/llvm/Analysis/AliasAnalysis.h

@@ -64,7 +64,6 @@ class LoopInfo;
 class PreservedAnalyses;
 class TargetLibraryInfo;
 class Value;
-template <typename> class SmallPtrSetImpl;
 
 /// The possible results of an alias query.
 ///

llvm/include/llvm/Analysis/AliasAnalysisEvaluator.h

@@ -29,7 +29,6 @@
 namespace llvm {
 class AAResults;
 class Function;
-class FunctionPass;
 
 class AAEvaluator : public PassInfoMixin<AAEvaluator> {
   int64_t FunctionCount = 0;

llvm/include/llvm/Analysis/InstructionSimplify.h

@@ -45,7 +45,6 @@ class DominatorTree;
 class Function;
 class Instruction;
 struct LoopStandardAnalysisResults;
-class MDNode;
 class Pass;
 template <class T, unsigned n> class SmallSetVector;
 class TargetLibraryInfo;