Bluetooth: Add proper response to mgmt_remove_keys command

Since the command can fail we need to have a proper response with the
remote address and a failure status for it. This also updates it to
conform to the latest mgmt API spec.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>