uas: Remove task-management / abort error handling code

uas: Remove task-management / abort error handling code

There are various bug reports about oopses / hangs with the uas driver,
which all point to the abort-command and logical-unit-reset (task-management)
error handling paths.

Getting these right is very hard, there are quite a few corner cases, and
testing is almost impossible since under normal operation these code paths
are not used at all.

Another problem is that there are also some cases where it simply is not clear
what to do at all. E.g. over usb-2 multiple outstanding commands share the same
endpoint. What if a command gets aborted while its sense urb is half way
through completing (so some data has been transfered but not all). Since the
urb is not yet complete we don't know if the sense urb is actually for this
command, or for one of the other oustanding commands. If it is for one of the
other commands and we cancel it, then we end up in an undefined state. But if
it is actually for the command we're aborting, and the abort succeeds, then it
may never complete...

This exact same problem applies to logical unit resets too, if there are
multiple luns, then commands outstanding on both luns share the sense
endpoint. If there is only a single lun, then doing a logical unit reset is
little better then doing a full usb device reset.

So summarizing because:
1) abort / lun-reset is very tricky to get right
2) Not being able to test the tricky code, which means it will have bugs
3) This being a code path which under normal operation will never happen,
   so being slow / sub-optimal here is not really an issue
4) Under error conditions we will still be able to recover through usb
   device resets.
5) This may be a bit slower in some cases, but this is actually faster in
   cases where the bridge ship has locked up, which seems to be the most
   common error case sofar.

This commit removes the abort / lun-reset error handling paths, and also the
taks-mgmt code since those are the only 2 task-mgmt users. Leaving only the
(tested and testable) usb-device-reset error handling path in place.

Note I realize that this is somewhat of a big hammer, but currently people
are seeing very hard to debug oopses with uas. First let focus on making uas
work reliable, then we can later look into adding more fine grained error
handling.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>