ath6kl: revert USB support

The ath6kl driver is causing build failures when the ath6kl bits are
not built as modules.  A better fix is forthcoming in a future release,
but for now lets revert the problematic code.

This reverts the following commits:

	fde57764
	d70385a2
	59d954dd



Signed-off-by: John W. Linville <linville@tuxdriver.com>