adb_probe_task: remove unneeded flush_signals() call

adb_probe_task() is forked by "events" thread, all signals are ignored, no
need to play with signal blocking/flushing.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>