swiotlb-xen: drop DEFAULT_NSLABS

It was introduced by 4035b43d ("xen-swiotlb: remove xen_set_nslabs")
and then not removed by 2d29960a ("swiotlb: dynamically allocate
io_tlb_default_mem").
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

Link: https://lore.kernel.org/r/15259326-209a-1d11-338c-5018dc38abe8@suse.comSigned-off-by: Juergen Gross <jgross@suse.com>

drivers/xen/swiotlb-xen.c

@@ -152,8 +152,6 @@ static const char *xen_swiotlb_error(enum xen_swiotlb_err err)
 	return "";
 }
 
-#define DEFAULT_NSLABS		ALIGN(SZ_64M >> IO_TLB_SHIFT, IO_TLB_SEGSIZE)
-
 int xen_swiotlb_init(void)
 {
 	enum xen_swiotlb_err m_ret = XEN_SWIOTLB_UNKNOWN;