Bluetooth: Remove unused hci_le_ltk_reply()

In this API, we were using sizeof operator for an array
given as function argument, which is invalid.
However this API is not used anywhere.

Change-Id: I80a43472b35f0f6c117624de2b2907b37eefb786
Signed-off-by: Syam Sidhardhan <s.syam@samsung.com>