qcacmn: Replace duplicate api's of vdev_connected

Currently, the vdev connection status is checked by getting
the bss peer of that vdev, and if the bss peer is in associated
state then vdev connected status is sent as true. It can happen
vdev is present and bss peer is deleted after getting the bss peer
from vdev pointer. Then bss peer can not be dereferenced to get the
its status.

Instead remove all the duplicate api's tdls_is_vdev_connected,
pmo_core_is_vdev_connected, and wlan_vdev_is_connected with
wlan_vdev_is_up. wlan_vdev_is_up gives success status
if associated.

Change-Id: I863c3c0689f329870bd08c813813c16956135209
CRs-Fixed: 2426092