Clean up unused operator_warning

    <!-- Format for a summary describing the amount of data before the user is warned or limited [CHAR LIMIT=NONE] -->

    <string name="cell_data_warning_and_limit"><xliff:g name="amount" example="1 GB">^1</xliff:g> data warning / <xliff:g name="amount" example="2 GB">^2</xliff:g> data limit</string>

    <!-- A summary shown on data usage screens to indicate inaccuracy of data tracking [CHAR LIMIT=NONE] -->

    <string name="operator_warning">Carrier data accounting may differ from device accounting</string>

    <!-- A summary shown on data usage screens to indicate data tracking excluded from carrier networks [CHAR LIMIT=NONE] -->

    <string name="non_carrier_data_usage_warning">Excludes data used by carrier networks</string>

        <com.android.settings.datausage.ChartDataUsagePreference

            android:key="chart_data" />

        <Preference

            android:key="operator_warning"

            android:summary="@string/operator_warning"

            android:selectable="false" />

        <Preference

            android:key="non_carrier_data_usage_warning"

            android:summary="@string/non_carrier_data_usage_warning"

        mChart = findPreference(KEY_CHART_DATA);

        mApps = findPreference(KEY_APPS_GROUP);

        final Preference unnecessaryWarningPreference = findPreference("operator_warning");

        if (unnecessaryWarningPreference != null) {

            unnecessaryWarningPreference.setVisible(false);

        }

        processArgument();

        updateSubscriptionInfoEntity();

        mDataStateListener = new MobileDataEnabledListener(activity, this);