Hide CellularBatteryStats#getTxTimeMillis.

Will be re-exposed as SystemApi in S.

Test: TH
Bug: 152247297
Change-Id: Ifb87676fa5afd2720dd09f36f3ff67c1b215b676
diff --git a/api/system-current.txt b/api/system-current.txt
index 6e336a8..82b49b7 100755
--- a/api/system-current.txt
+++ b/api/system-current.txt
@@ -8755,7 +8755,6 @@
     method public long getSleepTimeMillis();
     method @NonNull public long getTimeInRatMicros(int);
     method @NonNull public long getTimeInRxSignalStrengthLevelMicros(@IntRange(from=android.telephony.CellSignalStrength.SIGNAL_STRENGTH_NONE_OR_UNKNOWN, to=android.telephony.CellSignalStrength.SIGNAL_STRENGTH_GREAT) int);
-    method @NonNull public long getTxTimeMillis(@IntRange(from=android.telephony.ModemActivityInfo.TX_POWER_LEVEL_0, to=android.telephony.ModemActivityInfo.TX_POWER_LEVEL_4) int);
     method public void writeToParcel(@NonNull android.os.Parcel, int);
     field @NonNull public static final android.os.Parcelable.Creator<android.os.connectivity.CellularBatteryStats> CREATOR;
   }
diff --git a/core/java/android/os/connectivity/CellularBatteryStats.java b/core/java/android/os/connectivity/CellularBatteryStats.java
index 633b374..121fd33 100644
--- a/core/java/android/os/connectivity/CellularBatteryStats.java
+++ b/core/java/android/os/connectivity/CellularBatteryStats.java
@@ -315,6 +315,8 @@
      * <li> index 3 = 15dBm < tx_power < 20dBm. </li>
      * <li> index 4 = tx_power > 20dBm. </li>
      * </ul>
+     *
+     * @hide
      */
     @NonNull
     public long getTxTimeMillis(