Fix some Bluetooth settings bugs.

- Remove BluetoothFindNearby.java (no longer used)
- Show message when Bluetooth is turning off
- Fix case where device name sometimes didn't show when turning BT on
- Disable "Rename device" and "Visibility timeout" menus when BT is off
- Remove "Got onDeviceAdded, but cachedDevice already exists" log message
- Never show "Rename device" in action menu (bug 5064378)
- Show discovery time remaining as "m:ss", not "mm:ss" (bug 5064104)

Bug: 5064378
Bug: 5064104
Change-Id: I79609dfdad61993a28cff64c9e082870ff74d180