anv: remove list items on batch fini

This doesn't seem to fix anything because those destroy() calls happen
right before the command buffer object & its list of batch_bo is also
destroyed. Still looks a bit cleaner.

v2: Found a second occurence

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net> (v2)
Fixes: 26ba0ad5 ("vk: Re-name command buffer implementation files")
Cc: <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 935f8f0e)