feat: Remove .env file for AI Scribe

It was used at the beginning for configuration purpose but now we
have the JMAP capability, no need anymore.

lib/features/composer/presentation/mixin/ai_scribe_in_composer_mixin.dart

@@ -23,8 +23,6 @@ mixin AIScribeInComposerMixin {
   AccountId? get accountId;
 
   bool get isAIScribeAvailable {
-    if (!AIConfig.isAiEnabled) return false;
-
     final currentSession = session;
     final currentAccountId = accountId;