Removed XCallbackParameters and related code.

ios/chrome/browser/xcallback_parameters.mm

-// Copyright 2012 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.
-
-#import "ios/chrome/browser/xcallback_parameters.h"
-
-#if !defined(__has_feature) || !__has_feature(objc_arc)
-#error "This file requires ARC support."
-#endif
-
-namespace {
-NSString* const kSourceAppIdKey = @"sourceAppId";
-}
-
-@implementation XCallbackParameters
-@synthesize sourceAppId = _sourceAppId;
-
-- (instancetype)initWithSourceAppId:(NSString*)sourceAppId {
-  self = [super init];
-  if (self) {
-    _sourceAppId = [sourceAppId copy];
-  }
-  return self;
-}
-
-- (NSString*)description {
-  return [NSString stringWithFormat:@"SourceApp: %@\n", _sourceAppId];
-}
-
-#pragma mark - NSCoding Methods
-
-- (instancetype)initWithCoder:(NSCoder*)aDecoder {
-  return
-      [self initWithSourceAppId:[aDecoder decodeObjectForKey:kSourceAppIdKey]];
-}
-
-- (void)encodeWithCoder:(NSCoder*)aCoder {
-  [aCoder encodeObject:_sourceAppId forKey:kSourceAppIdKey];
-}
-
-#pragma mark - NSCopying Methods
-
-- (instancetype)copyWithZone:(NSZone*)zone {
-  return [[[self class] allocWithZone:zone] initWithSourceAppId:_sourceAppId];
-}
-
-@end