The dcssblk driver was the last user of FS_DAX_LIMITED. That was marked
broken by 653d7825c149 ("dcssblk: mark DAX broken, remove FS_DAX_LIMITED
support") to allow removal of PFN_SPECIAL. However the FS_DAX_LIMITED
config option itself was not removed, so do that now.
Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>