refactor: MainActivity 불필요한 주석 제거

android/app/src/main/kotlin/com/naturebridgeai/digitalrentmanager/MainActivity.kt

@@ -2,7 +2,4 @@ package com.naturebridgeai.digitalrentmanager
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity: FlutterActivity()
-    // flutter_sms_inbox 패키지가 SMS 처리를 담당하므로
-    // 기존 MethodChannel 코드는 제거되었습니다
-}