Revert "Bluetooth: Fix possible deadlock in SCO code"

This reverts commit 269c4845.

The commit was causing dead locks and NULL dereferences in the sco code:

 [28084.104013] BUG: soft lockup - CPU#0 stuck for 22s! [kworker/u:0H:7]
 [28084.104021] Modules linked in: btusb bluetooth <snip [last unloaded:
bluetooth]
...
 [28084.104021]  [<c160246d>] _raw_spin_lock+0xd/0x10
 [28084.104021]  [<f920e708>] sco_conn_del+0x58/0x1b0 [bluetooth]
 [28084.104021]  [<f920f1a9>] sco_connect_cfm+0xb9/0x2b0 [bluetooth]
 [28084.104021]  [<f91ef289>]
hci_sync_conn_complete_evt.isra.94+0x1c9/0x260 [bluetooth]
 [28084.104021]  [<f91f1a8d>] hci_event_packet+0x74d/0x2b40 [bluetooth]
 [28084.104021]  [<c1501abd>] ? __kfree_skb+0x3d/0x90
 [28084.104021]  [<c1501b46>] ? kfree_skb+0x36/0x90
 [28084.104021]  [<f91fcb4e>] ? hci_send_to_monitor+0x10e/0x190 [bluetooth]
 [28084.104021]  [<f91fcb4e>] ? hci_send_to_monitor+0x10e/0x190 [bluetooth]

Cc: stable@vger.kernel.org
Reported-by: Chan-yeol Park <chanyeol.park@gmail.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>