Remove the device from le backgrond connection whitelist when it's unpaired

this is due to we didn't remove the device from the white list before unpair
Which cause a fake pair request from remote device triggered
right after the acl is disconnected.
The fix is to remove the BLE device from whitelist before unpair.
Also fix a problem return wrong device handle from bta_hh_le_add_device.

if bta_hh_le_add_device is called right after reboot, before we connect HID device.
This is normally true for a previous paired device, which we saved in the nvram.
The wrong device handle will cause the removing HID device from while list failed
after unpair the HID device.

bug:11676338
Change-Id: Id5b45b2829da9a990dfd1dbae0c15764b16c2bfb