LU-11825 llite: Remove ptask framework

LU-11825 llite: Remove ptask framework

With the removal of pio, the ptask framework no longer has
any users.

Signed-off-by: Patrick Farrell <paf@cray.com>
Change-Id: Id3237740c251b01bc176967f8fe5fd12bb82f553
Reviewed-on: https://review.whamcloud.com/33913
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@gmail.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>