use a static map for additional headers

packages/stream_chat/lib/version.dart

@@ -1,22 +1,10 @@
 import 'package:stream_chat/src/client/client.dart';
-import 'package:stream_chat/src/core/platform_detector/platform_detector.dart';
 
 /// Current package version
 /// Used in [StreamChatClient] to build the `x-stream-client` header
 // ignore: constant_identifier_names
 const PACKAGE_VERSION = '3.2.0';
 
-/// Default user agent used for the 'x-stream-client' header
-final defaultUserAgent = 'stream-chat-dart-client-'
-    '${CurrentPlatform.name}-'
-    '${PACKAGE_VERSION.split('+')[0]}';
-
-/// Current used package
-/// This is used to set the `x-stream-client` header using info about
-/// the package in use
-/// For example: llc/core/ui
-Package usedPackage = Package.llc;
-
 /// Possible packages
 enum Package {
   /// The Low Level Client