Remove the dynamic summary for bt preference.

Starting from b/62069132, we should use static summary for it.

Change-Id: I8ba5a9d6e8b5bcbcd9f4369cdf44004d557257a3
Fixes: 79666649
Test: Manual

src/com/android/settings/TetherSettings.java

@@ -387,7 +387,6 @@ public class TetherSettings extends RestrictedSettingsFragment
             if (adapter.getState() == BluetoothAdapter.STATE_OFF) {
                 mBluetoothEnableForTether = true;
                 adapter.enable();
-                mBluetoothTether.setSummary(R.string.bluetooth_turning_on);
                 mBluetoothTether.setEnabled(false);
                 return;
             }