Remove unused benchmark activity

Use minibench from pytorch/executorch repo

Author: kirklandsign

llm/android/LlamaDemo/app/src/main/AndroidManifest.xml

@@ -71,15 +71,6 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
-
-        <activity
-            android:name=".LlmBenchmarkRunner"
-            android:exported="true">
-            <intent-filter>
-                <action android:name="com.example.executorchllamademo.BENCHMARK" />
-            </intent-filter>
-        </activity>
-
     </application>
 
 </manifest>