components: Cleanup class/struct fwd declarations

components/rappor/reports.h

 // Copyright 2015 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 COMPONENTS_RAPPOR_REPORTS_H_
 #define COMPONENTS_RAPPOR_REPORTS_H_
 
 #include "components/rappor/reports.h"
 
 #include "components/rappor/byte_vector_utils.h"
 
 namespace rappor {
 
-struct RapporParameters;
-
 namespace internal {
 
 // Generate a randomized report for a single metric/field.
 ByteVector GenerateReport(const std::string& secret,
                           const NoiseParameters& parameters,
                           const ByteVector& value);
 
 }  // namespace internal
 
 }  // namespace rappor
 
 #endif  // COMPONENTS_RAPPOR_REPORTS_H_