Bluetooth: Remove useless flush_work() causing lockdep warnings

The calls to flush_work() are pointless in a single thread workqueue
and they are actually causing a lockdep warning.

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[ INFO: possible recursive locking detected ]
2.6.30-rc6-02911-gbb803cfb #16
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bluetooth/2518 is trying to acquire lock:
 (bluetooth){+.+.+.}, at: [<c0130c14>] flush_work+0x28/0xb0

but task is already holding lock:
 (bluetooth){+.+.+.}, at: [<c0130424>] worker_thread+0x149/0x25e

other info that might help us debug this:
2 locks held by bluetooth/2518:
 #0:  (bluetooth){+.+.+.}, at: [<c0130424>] worker_thread+0x149/0x25e
 #1:  (&conn->work_del){+.+...}, at: [<c0130424>] worker_thread+0x149/0x25e

stack backtrace:
Pid: 2518, comm: bluetooth Not tainted 2.6.30-rc6-02911-gbb803cfb #16
Call Trace:
 [<c03d64d9>] ? printk+0xf/0x11
 [<c0140d96>] __lock_acquire+0x7ce/0xb1b
 [<c0141173>] lock_acquire+0x90/0xad
 [<c0130c14>] ? flush_work+0x28/0xb0
...