refactor: Remove unused dependencies

lib/utils/get_client_secret.dart

@@ -1,7 +0,0 @@
-import 'dart:math';
-
-const _chars = 'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz1234567890';
-Random _rnd = Random();
-
-String getClientSecret(int length) => String.fromCharCodes(Iterable.generate(
-    length, (_) => _chars.codeUnitAt(_rnd.nextInt(_chars.length))));

lib/utils/matrix_sdk_extensions.dart/client_presence_extension.dart

@@ -1,30 +0,0 @@
-import 'package:matrix/matrix.dart';
-
-extension ClientPresenceExtension on Client {
-  List<CachedPresence> get contactList {
-    final directChatsMxid = rooms
-        .where((r) => r.isDirectChat)
-        .map((r) => r.directChatMatrixID)
-        .toSet();
-    final contactList = directChatsMxid
-        .map(
-          (mxid) =>
-              presences[mxid] ??
-              CachedPresence(
-                PresenceType.offline,
-                0,
-                null,
-                false,
-                mxid ?? '',
-              ),
-        )
-        .toList();
-
-    contactList.sort((a, b) => a.userid.compareTo(b.userid));
-    contactList.sort((a, b) => ((a.lastActiveTimestamp ??
-            DateTime.fromMillisecondsSinceEpoch(0))
-        .compareTo(
-            b.lastActiveTimestamp ?? DateTime.fromMillisecondsSinceEpoch(0))));
-    return contactList;
-  }
-}