I've been trying to do this..but
Torch isn't an app, it's part of MiuiSystemUI.apk like fonfon said.
Here's:
<activity android:theme="@android:style/Theme.NoTitleBar" android:label="@string/torch_activity_name" android:icon="@drawable/torch_activity_icon" android:name=".TorchActivity" android:taskAffinity="" android:launchMode="singleTask" android:screenOrientation="portrait">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
That's part of AndroidManifest.xml from MiuiSystemUI.apk which include the Torch Activity (ACTIVITY not app) so you'd need to modify the androidmanifest, but that requires resigning the apk, and if you re-sign it, it will be incompatible with android.system...so it isn't easy to remove...