[ConstraintSystem] NFC: remove obsolete transferExprTypes

(cherry picked from commit 11e1d13)

Author: xedin

lib/Sema/ConstraintSystem.h

@@ -1326,30 +1326,6 @@ class ConstraintSystem {
     bool walkToDeclPre(Decl *decl) override { return false; }
   };
 
-  class TransferExprTypes : public ASTWalker {
-    ConstraintSystem &toCS;
-    ConstraintSystem &fromCS;
-
-  public:
-    TransferExprTypes(ConstraintSystem &toCS, ConstraintSystem &fromCS)
-        : toCS(toCS), fromCS(fromCS) {}
-
-    Expr *walkToExprPost(Expr *expr) override {
-      if (fromCS.hasType(expr))
-        toCS.setType(expr, fromCS.getType(expr));
-
-      return expr;
-    }
-
-    /// \brief Ignore statements.
-    std::pair<bool, Stmt *> walkToStmtPre(Stmt *stmt) override {
-      return { false, stmt };
-    }
-
-    /// \brief Ignore declarations.
-    bool walkToDeclPre(Decl *decl) override { return false; }
-  };
-
 public:
 
   void setExprTypes(Expr *expr) {
@@ -1375,10 +1351,6 @@ class ConstraintSystem {
     expr->walk(CacheExprTypes(expr, *this, excludeRoot));
   }
 
-  void transferExprTypes(ConstraintSystem *oldCS, Expr *expr) {
-    expr->walk(TransferExprTypes(*this, *oldCS));
-  }
-
   /// \brief The current solver state.
   ///
   /// This will be non-null when we're actively solving the constraint