Bluetooth: Move Delete Stored Link Key to 4th phase of initialization

This moves the execution of Delete Stored Link Key command to the
hci_init4_req phase. No actual code has been changed. The command
is just executed at a later stage of the initialization.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>