Bluetooth: Remove unused hci_le_ltk_neg_reply()

No one is using hci_le_ltk_neg_reply() in bluetooth subsystem.

Conflicts:
	include/net/bluetooth/hci_core.h

Signed-off-by: Syam Sidhardhan <s.syam@samsung.com>
Signed-off-by: Gustavo Padovan <gustavo@padovan.org>

Change-Id: I625cd396c470c6210b4a241dfebe02f0af752588