aio: remove unnecessary debugging from aio_free_ring()

The commit 36bc08cc0170 ("fs/aio: Add support to aio ring pages migration")
added some debugging code that is not required and resulted in a build error
when 98474236f72e ("vfs: make the dentry cache use the lockref infrastructure")
was added to the tree.  The code is not required, so just delete it.

Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>