batman-adv: Remove unused declarations

Since commit 335fbe0f ("batman-adv: tvlv - convert tt query packet to use tvlv unicast packets")
batadv_recv_tt_query() is not used.
And commit 122edaa0 ("batman-adv: tvlv - convert roaming adv packet to use tvlv unicast packets")
left behind batadv_recv_roam_adv().

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>