ar9170usb: remove deprecated aggregation code

This patch removes the incomplete AMPDU implementation in ar9170usb.

The code in question is:
 * too big and complex (more than 550 SLOC.)
   This is enough to qualify for a new separate code file!

 * unbalanced quantity & quality
	over-engineered areas like:
		* xmit scheduling and queuing frames for multiple HT peers
		* redundant frame sorting
	are confronted by gaping holes:
		* accurate transmission feedback
		* firmware error-handling and device reset
		* HT rate control algorithm

 * error-prone
	Since its inclusion, hardly anything was done to fix
	any of the outlined flaws from the initial commit message.

   => This also indicates poor maintainability.

 * relies heavily on several spinlocks.

As a result of this shortcomings, the code is slow and does not
even support the most basic 11n requirement: HT station mode.

Therefore, I request to purge my heap of **** from the kernel:
"ar9170: implement transmit aggregation".

The next item on the agenda is: (re-)start from scratch with
an adequate design to accommodate the special requirements
and features of the available frameworks and tools.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>