staging: wfx: remove false positive warning

staging: wfx: remove false positive warning

When a station is removed, the driver check that all the Tx frames were
correctly sent. However, the station can be removed before all the Tx
frames were acknowledged and a false positive warning can be emitted.

The previous commit has added a trace when driver received an
acknowledge for a non-existent station. It appear that these events
are perfectly correlated and there is no leak.

Now, the subject is perfectly understood. Remove the warning. Just keep
a debug trace in case we have any doubt in the future.

In the past, the subject has already been discussed here:
   https://lore.kernel.org/driverdev-devel/6287924.ghGFUMk3OD@pc-42/

Fixes: 4bbc6a3e7ad0 ("staging: wfx: make warning about pending frame less scary")
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200515083325.378539-20-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>