Cleanup remaining class/struct fwd declarations

sandbox/linux/bpf_dsl/bpf_dsl_forward.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SANDBOX_LINUX_BPF_DSL_BPF_DSL_FORWARD_H_
 #define SANDBOX_LINUX_BPF_DSL_BPF_DSL_FORWARD_H_
 
 #include <memory>
 
 #include "sandbox/sandbox_export.h"
 
 namespace sandbox {
 namespace bpf_dsl {
 
 // The bpf_dsl_forward.h header provides forward declarations for the
 // types defined in bpf_dsl.h. It's intended for use in user headers
 // that need to reference bpf_dsl types, but don't require definitions.
 
 namespace internal {
 class ResultExprImpl;
 class BoolExprImpl;
 }
 
 using ResultExpr = std::shared_ptr<const internal::ResultExprImpl>;
 using BoolExpr = std::shared_ptr<const internal::BoolExprImpl>;
 
-template <typename T>
-class Arg;
-
-class Elser;
-
-template <typename T>
-class Caser;
-
 }  // namespace bpf_dsl
 }  // namespace sandbox
 
 namespace std {
 extern template class SANDBOX_EXPORT
     shared_ptr<const sandbox::bpf_dsl::internal::BoolExprImpl>;
 extern template class SANDBOX_EXPORT
     shared_ptr<const sandbox::bpf_dsl::internal::ResultExprImpl>;
 }  // namespace std
 
 #endif  // SANDBOX_LINUX_BPF_DSL_BPF_DSL_FORWARD_H_