chore: remove unnecessary ChannelTheme class

packages/stream_chat_flutter/lib/src/theme/channel_header_theme.dart

@@ -36,7 +36,7 @@ class ChannelHeaderTheme extends InheritedTheme {
     final channelHeaderTheme =
         context.dependOnInheritedWidgetOfExactType<ChannelHeaderTheme>();
     return channelHeaderTheme?.data ??
-        StreamChatTheme.of(context).channelTheme.channelHeaderTheme;
+        StreamChatTheme.of(context).channelHeaderTheme;
   }
 
   @override

packages/stream_chat_flutter/lib/src/theme/channel_theme.dart

@@ -1,28 +0,0 @@
-import 'package:stream_chat_flutter/src/theme/channel_header_theme.dart';
-
-/// Channel theme data
-class ChannelTheme {
-  /// Constructor for creating [ChannelTheme]
-  ChannelTheme({
-    required this.channelHeaderTheme,
-  });
-
-  /// Theme of the [ChannelHeader] widget
-  final ChannelHeaderThemeData channelHeaderTheme;
-
-  /// Creates a copy of [ChannelTheme] with specified attributes overridden.
-  ChannelTheme copyWith({
-    ChannelHeaderThemeData? channelHeaderTheme,
-  }) =>
-      ChannelTheme(
-        channelHeaderTheme: channelHeaderTheme ?? this.channelHeaderTheme,
-      );
-
-  /// Merge with theme
-  ChannelTheme merge(ChannelTheme? other) {
-    if (other == null) return this;
-    return copyWith(
-      channelHeaderTheme: channelHeaderTheme.merge(other.channelHeaderTheme),
-    );
-  }
-}

packages/stream_chat_flutter/lib/src/theme/themes.dart

@@ -3,7 +3,6 @@ export 'channel_header_theme.dart';
 export 'channel_list_header_theme.dart';
 export 'channel_list_view_theme.dart';
 export 'channel_preview_theme.dart';
-export 'channel_theme.dart';
 export 'color_theme.dart';
 export 'gallery_footer_theme.dart';
 export 'gallery_header_theme.dart';