mwifiex: remove AMSDU_AGGR_CTRL command response handler

HostCmd_CMD_AMSDU_AGGR_CTRL is never called with GET action.
So the code in mwifiex_ret_amsdu_aggr_ctrl() becomes redundant.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>