dax: Remove an unused field in struct dax_operations

.dax_supported() was apparently removed by commit 7b0800d0 ("dax:
remove dax_capable") on 2021-11.

Remove the now unused function pointer from the struct dax_operations.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/56b92b722ca0a6fd1387c871a6ec01bcb9bd525e.1725203804.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Ira Weiny <ira.weiny@intel.com>