Revert "net: ipv6: add fib6_nh_release_dsts stub"

This reverts commit cca61bb1 which is
commit 8837cbbf854246f5f4d565f21e6baa945d37aded upstream.

It breaks the abi and is not needed for Android systems, so it can be
safely reverted.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I25198224e60cb4de5c9e5186331c78e2e4c9c28c